I don’t have any Twilio DIDs, but I would assume that there is a place where you enter
sip:11.22.33.44
or
sip:mypbx.mycompany.com
Have you tried changing that to
sip:11.22.33.44:5160
or
sip:mypbx.mycompany.com:5160
?
If it didn’t work, provide details (error message when entered, change had no effect, FreePBX gave a different error, etc.)
BTW, given that Twilio sends calls from multiple IP addresses (therefore requiring multiple chan_sip trunks), why didn’t you just use a pjsip trunk for Twilio, where you can simply list the addresses in the match field?