Dialing extension, one biggest hassles, never been able to figure out how to do the auto trick. This links explains ok:

https://www.payetteforward.com/add-an-extension-to-iphone-contact-heres-fix/

Finally worked with one bank, but then another bank did not work. not sure why not.

Not sure matters at all but: can you put comma in phone or desktop version of contact same/ ok? Can put comma in with keyboard comma or have to be the + method with iphone keyboard only? o r not matter? Is odd or normal works with some places not others? Any others explore this? thanks.