diff --git a/src/chainparams.cpp b/src/chainparams.cpp
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -137,7 +137,7 @@
         consensus.gravitonHeight = 609135;
 
         // May 15, 2020 12:00:00 UTC protocol upgrade
-        consensus.phononActivationTime = 1589544000;
+        consensus.phononHeight = 635258;
 
         // Nov 15, 2020 12:00:00 UTC protocol upgrade
         consensus.axionActivationTime = 1605441600;
@@ -341,7 +341,7 @@
         consensus.gravitonHeight = 1341711;
 
         // May 15, 2020 12:00:00 UTC protocol upgrade
-        consensus.phononActivationTime = 1589544000;
+        consensus.phononHeight = 1378460;
 
         // Nov 15, 2020 12:00:00 UTC protocol upgrade
         consensus.axionActivationTime = 1605441600;
@@ -494,7 +494,7 @@
         consensus.gravitonHeight = 0;
 
         // May 15, 2020 12:00:00 UTC protocol upgrade
-        consensus.phononActivationTime = 1589544000;
+        consensus.phononHeight = 0;
 
         // Nov 15, 2020 12:00:00 UTC protocol upgrade
         consensus.axionActivationTime = 1605441600;
diff --git a/src/consensus/activation.cpp b/src/consensus/activation.cpp
--- a/src/consensus/activation.cpp
+++ b/src/consensus/activation.cpp
@@ -62,13 +62,17 @@
     return IsGravitonEnabled(params, pindexPrev->nHeight);
 }
 
+static bool IsPhononEnabled(const Consensus::Params &params, int32_t nHeight) {
+    return nHeight >= params.phononHeight;
+}
+
 bool IsPhononEnabled(const Consensus::Params &params,
                      const CBlockIndex *pindexPrev) {
     if (pindexPrev == nullptr) {
         return false;
     }
 
-    return pindexPrev->GetMedianTimePast() >= params.phononActivationTime;
+    return IsPhononEnabled(params, pindexPrev->nHeight);
 }
 
 bool IsAxionEnabled(const Consensus::Params &params,
diff --git a/src/consensus/params.h b/src/consensus/params.h
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -78,8 +78,8 @@
     int magneticAnomalyHeight;
     /** Block height at which the graviton activation becomes active */
     int gravitonHeight;
-    /** Unix time used for MTP activation of 15 May 2020 12:00:00 UTC upgrade */
-    int phononActivationTime;
+    /** Block height at which the phonon activation becomes active */
+    int phononHeight;
     /** Unix time used for MTP activation of 15 Nov 2020 12:00:00 UTC upgrade */
     int axionActivationTime;
     /** Unix time used for MTP activation of 15 May 2021 12:00:00 UTC upgrade */
diff --git a/src/test/activation_tests.cpp b/src/test/activation_tests.cpp
--- a/src/test/activation_tests.cpp
+++ b/src/test/activation_tests.cpp
@@ -42,26 +42,19 @@
 }
 
 BOOST_AUTO_TEST_CASE(isphononenabled) {
-    const Consensus::Params &params = Params().GetConsensus();
-    const auto activation = params.phononActivationTime;
-    SetMockTime(activation - 1000000);
-
-    BOOST_CHECK(!IsPhononEnabled(params, nullptr));
+    const Consensus::Params &consensus = Params().GetConsensus();
+    BOOST_CHECK(!IsPhononEnabled(consensus, nullptr));
 
-    std::array<CBlockIndex, 12> blocks;
+    std::array<CBlockIndex, 4> blocks;
+    blocks[0].nHeight = consensus.phononHeight - 2;
     for (size_t i = 1; i < blocks.size(); ++i) {
         blocks[i].pprev = &blocks[i - 1];
+        blocks[i].nHeight = blocks[i - 1].nHeight + 1;
     }
-    BOOST_CHECK(!IsPhononEnabled(params, &blocks.back()));
-
-    SetMTP(blocks, activation - 1);
-    BOOST_CHECK(!IsPhononEnabled(params, &blocks.back()));
-
-    SetMTP(blocks, activation);
-    BOOST_CHECK(IsPhononEnabled(params, &blocks.back()));
-
-    SetMTP(blocks, activation + 1);
-    BOOST_CHECK(IsPhononEnabled(params, &blocks.back()));
+    BOOST_CHECK(!IsPhononEnabled(consensus, &blocks[0]));
+    BOOST_CHECK(!IsPhononEnabled(consensus, &blocks[1]));
+    BOOST_CHECK(IsPhononEnabled(consensus, &blocks[2]));
+    BOOST_CHECK(IsPhononEnabled(consensus, &blocks[3]));
 }
 
 BOOST_AUTO_TEST_CASE(isaxionenabled) {