When a contact import mapped a Phone Type column and the cell was empty, the number was stored as Mobile. The review screen showed the cell blank, so there was nothing to say the value had been chosen for you.
Phone type is what tells you whether a number can receive a text, so this turned missing information into a confident answer. It mattered most on purchased or skip-traced lists, where the provider often does not say what kind of line a number is and a large share of them are landlines — those numbers all arrived labelled Mobile.
An empty Phone Type cell now imports as no type at all, which the contact record shows as Other. An unmapped Phone Type column behaves the same way, rather than assuming every imported number is a cell phone. Values you do supply are unchanged: Mobile, Home, Work, Fax, Main, Support, Sales, Toll Free and Other all import as themselves, and common spellings from Apple, Google and Outlook exports are still recognised.
This applies to imports run from now on. Numbers already imported and stored as Mobile are not changed, because there is no way to tell them apart from numbers that really are mobiles.