Trigger from a legato MIDI source

Trying to build a monophonic synth rack and want to get a trigger to reset the LFO phase from the MIDI notes. However I don't want to have it retrigger on every note. The synth portion itself handles the legato mode just fine, but I want to get a trigger that only occurs when the first MIDI Note On event happens and ignores additional MIDI Note On events until it gets a corresponding MIDI Note Off event while there isn't another MIDI Note held

Is there a rack that does this or do I have to make my own?