diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -462,6 +462,7 @@
 	noui.cpp
 	outputtype.cpp
 	policy/fees.cpp
+	policy/mempool.cpp
 	policy/policy.cpp
 	pow.cpp
 	rest.cpp
diff --git a/src/Makefile.am b/src/Makefile.am
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -282,6 +282,7 @@
   noui.cpp \
   outputtype.cpp \
   policy/fees.cpp \
+  policy/mempool.cpp \
   policy/policy.cpp \
   pow.cpp \
   rest.cpp \
diff --git a/src/Makefile.test.include b/src/Makefile.test.include
--- a/src/Makefile.test.include
+++ b/src/Makefile.test.include
@@ -109,6 +109,7 @@
   test/lcg_tests.cpp \
   test/lcg.h \
   test/limitedmap_tests.cpp \
+  test/mempool_policy_tests.cpp \
   test/mempool_tests.cpp \
   test/merkle_tests.cpp \
   test/merkleblock_tests.cpp \
diff --git a/src/policy/mempool.h b/src/policy/mempool.h
--- a/src/policy/mempool.h
+++ b/src/policy/mempool.h
@@ -4,8 +4,16 @@
 #ifndef BITCOIN_POLICY_MEMPOOL_H
 #define BITCOIN_POLICY_MEMPOOL_H
 
+#include <cstdint>
+
+class CBlockIndex;
+namespace Consensus {
+struct Params;
+}
+
 /** Default for -limitancestorcount, max number of in-mempool ancestors */
 static const unsigned int DEFAULT_ANCESTOR_LIMIT = 25;
+static const unsigned int DEFAULT_ANCESTOR_LIMIT_LONGER = 50;
 /**
  * Default for -limitancestorsize, maximum kilobytes of tx + all in-mempool
  * ancestors.
@@ -13,10 +21,17 @@
 static const unsigned int DEFAULT_ANCESTOR_SIZE_LIMIT = 101;
 /** Default for -limitdescendantcount, max number of in-mempool descendants */
 static const unsigned int DEFAULT_DESCENDANT_LIMIT = 25;
+static const unsigned int DEFAULT_DESCENDANT_LIMIT_LONGER = 50;
 /**
  * Default for -limitdescendantsize, maximum kilobytes of in-mempool
  * descendants.
  */
 static const unsigned int DEFAULT_DESCENDANT_SIZE_LIMIT = 101;
 
+uint32_t GetDefaultAncestorLimit(const Consensus::Params &params,
+                                 const CBlockIndex *pindexPrev);
+
+uint32_t GetDefaultDescendantLimit(const Consensus::Params &params,
+                                   const CBlockIndex *pindexPrev);
+
 #endif // BITCOIN_POLICY_MEMPOOL_H
diff --git a/src/policy/mempool.cpp b/src/policy/mempool.cpp
new file mode 100644
--- /dev/null
+++ b/src/policy/mempool.cpp
@@ -0,0 +1,19 @@
+// Copyright (c) 2020 The Bitcoin developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <policy/mempool.h>
+
+#include <consensus/activation.h>
+
+uint32_t GetDefaultAncestorLimit(const Consensus::Params &params,
+                                 const CBlockIndex *pindexPrev) {
+    return IsPhononEnabled(params, pindexPrev) ? DEFAULT_ANCESTOR_LIMIT_LONGER
+                                               : DEFAULT_ANCESTOR_LIMIT;
+}
+
+uint32_t GetDefaultDescendantLimit(const Consensus::Params &params,
+                                   const CBlockIndex *pindexPrev) {
+    return IsPhononEnabled(params, pindexPrev) ? DEFAULT_DESCENDANT_LIMIT_LONGER
+                                               : DEFAULT_DESCENDANT_LIMIT;
+}
diff --git a/src/test/CMakeLists.txt b/src/test/CMakeLists.txt
--- a/src/test/CMakeLists.txt
+++ b/src/test/CMakeLists.txt
@@ -119,6 +119,7 @@
 		key_tests.cpp
 		lcg_tests.cpp
 		limitedmap_tests.cpp
+		mempool_policy_tests.cpp
 		mempool_tests.cpp
 		merkle_tests.cpp
 		merkleblock_tests.cpp
diff --git a/src/test/mempool_policy_tests.cpp b/src/test/mempool_policy_tests.cpp
new file mode 100644
--- /dev/null
+++ b/src/test/mempool_policy_tests.cpp
@@ -0,0 +1,54 @@
+// Copyright (c) 2019-2020 The Bitcoin developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <chain.h>
+#include <chainparams.h>
+#include <consensus/activation.h>
+#include <policy/mempool.h>
+#include <util/system.h>
+
+#include <test/test_bitcoin.h>
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_FIXTURE_TEST_SUITE(mempool_policy_tests, BasicTestingSetup)
+
+static void SetMTP(std::array<CBlockIndex, 12> &blocks, int64_t mtp) {
+    size_t len = blocks.size();
+
+    for (size_t i = 0; i < len; ++i) {
+        blocks[i].nTime = mtp + (i - (len / 2));
+    }
+
+    BOOST_CHECK_EQUAL(blocks.back().GetMedianTimePast(), mtp);
+}
+
+BOOST_AUTO_TEST_CASE(mempool_policy_activation_tests) {
+    CBlockIndex prev;
+
+    const Consensus::Params &params = Params().GetConsensus();
+    const auto activation =
+        gArgs.GetArg("-phononactivationtime", params.phononActivationTime);
+    SetMockTime(activation - 1000000);
+
+    std::array<CBlockIndex, 12> blocks;
+    for (size_t i = 1; i < blocks.size(); ++i) {
+        blocks[i].pprev = &blocks[i - 1];
+    }
+    SetMTP(blocks, activation - 1);
+    BOOST_CHECK(!IsPhononEnabled(params, &blocks.back()));
+    BOOST_CHECK_EQUAL(DEFAULT_ANCESTOR_LIMIT,
+                      GetDefaultAncestorLimit(params, &blocks.back()));
+    BOOST_CHECK_EQUAL(DEFAULT_DESCENDANT_LIMIT,
+                      GetDefaultDescendantLimit(params, &blocks.back()));
+
+    SetMTP(blocks, activation);
+    BOOST_CHECK(IsPhononEnabled(params, &blocks.back()));
+    BOOST_CHECK_EQUAL(DEFAULT_ANCESTOR_LIMIT_LONGER,
+                      GetDefaultAncestorLimit(params, &blocks.back()));
+    BOOST_CHECK_EQUAL(DEFAULT_DESCENDANT_LIMIT_LONGER,
+                      GetDefaultDescendantLimit(params, &blocks.back()));
+}
+
+BOOST_AUTO_TEST_SUITE_END()