Would this work (pedal testing)

[Mgt280y]

Starting to finish a few petals now but testing is not the easiest as I don't own/play guitar and settling up to try with the sax is a little awkward
I just downloaded
AƒG - Audio Function Generator. Powerful signal generator including sweeps and noise by Thomas Gruber
https://appsto.re/gb/QdKYT.i
Sorry if link doesn't work
I was thinking if I used this app on my iPhone on headphone socket 1/8 to 1/8 cable - 1/8 to 1/4 adaptor to in jack on pedal then output to headphones would this work?
Thanks Dan

[GibsonGM]

sure, it'll WORK, but we don't know a couple of things about it...such as its voltage output. You can find that out with a DMM. 
What is the output impedance?  (someone probably knows on here)...that may affect a few things (frequency).

But for rough and ready use, it will work.  Or you could build an easy 1 or 2 transistor oscillator, and dedicated it for this use.     There is no guarantee a pedal can drive headphones, by the way, so you may need to brew up a small (easy) headphone amp.  Not a big deal tho.

This can get you in the ballpark, so to speak, but won't really let you know how the pedal is coloring sound, like a guitar or sax - those are very complex wave forms.  But you'll hear phasing and distortion and such.