PHX: echo $input displays this: &_PHX_INTERNAL_&, how to get the value of this?

hi,
in a wayfinder chunk i wrote this

[+phx:input=`[+wf.docid+]`:myFunction+]

where myFunction is a phx snippet that echoes $input

but instead of displaying the doc id number like it would without the phx modifier,
it displays &_PHX_INTERNAL_&

I remember having resolved this issue and got to get the value of this phx variable but i can’t find it

does anyone know?