Digium Phones - HD codec (G.722 ?) - best supported sound quality please

I currently use ffmpeg to process files so that they will play on my Digium phones, I use:

the following options

-i inputfile.mp3 -acodec pcm_s16le -ac 1 -ar 8000 outputfile.wav

but would love to know if I can go higher/better as sometimes the converted file is crackly and the input isn’t.

Can I, for example, use the G.722 codec? Not sure how to go about this

thank you!

have you experimented with buffer sizes?

hmmm sorry to be dense, would that make a difference if a long file can play without crackles but a shorter file “with more going on” crackles? It seems to be if there is more depth to the sound then I might get crackles but if a simpler audio file then crackle free…