1) Can I say on the phone:
"Goodafternoon Ms[muz] Smith!"

Is this formal?

2) I introduce myself this way:

"Goodafternoon! I am calling from XXX company. My name is Jacob."

any other good versions?
Hello! This is Jacob (speaking). I'm calling from xxx company.

. . . . My name is Jacob."

If you want to be more formal, give your last name as well, eg My name is Jacob Smith.

Giving only your first name often makes you sound like a junior employee.