diff --git a/llvm/docs/Lexicon.rst b/llvm/docs/Lexicon.rst
--- a/llvm/docs/Lexicon.rst
+++ b/llvm/docs/Lexicon.rst
@@ -206,6 +206,9 @@
 P
 -
 
+**PHI**
+    `PHI <http://www.llvmpy.org/llvmpy-doc/dev/doc/llvm_concepts.html#ssa-form-and-phi-nodes>`_ node is the consequence of single assignment form in LLVM IR whose values depend on the operand corresponding to their dynamic predecessor basic block.
+
 **PR**
     Problem report. A bug filed on `the LLVM Bug Tracking System
     <https://bugs.llvm.org/enter_bug.cgi>`_.