Just guessing, set up a pjsip trunk with:
Trunk Name: Communico
Outbound CallerID: +390622223333
CID Options: Force Trunk CID
SIP Server: xx.yy.zz.87
SIP Server Port: 5060
The outbound caller ID format may need to be 390622223333 or 0622223333 (use the same format as on your 3CX system).
Set up an Outbound Route to send calls to the trunk using the correct format for the destination number.
Make a test call. If it doesn’t work (it probably won’t), at the Asterisk command prompt, type
pjsip set logger on
and make another failing test call. Paste the relevant section of the Asterisk log (redacted as desired) at pastebin.freepbx.org and post the link here.