Both two step authentication and two factor authentication can be set up to use text message or phone call verification to an arbitrary phone number.

According to this: https://support.apple.com/en-us/HT204915

a "trusted device" is only an Apple device, phone calls are for backup when you lose them. Even after that it's significant inconvenience in comparison to any other vendor using a standardized OTP approach working with any application that implements the standard. It's one of the little ways how Apple makes not owning an iOS device inconvenient for mac users.

It's extremely confusing, but Apple has two types of multple-factor authentication solutions in use.

The 'legacy' (my phrasing, only because it was the first implemented) MFA is SMS-based, and thus has not dependency on iPhones.

There's a newer (about a year or two old by this point) solution which has a 'richer user experience' and depends on having other Macs or iPhones to receive the MFA authentication dialogs.

The newer solution ("Two-factor authentication") also allows non-Apple phones to receive a code on their "trusted phone number". From the support page linked in a nearby comment:

What if I don’t have access to a trusted device or didn't receive a verification code?

If you're signing in and don’t have a trusted device handy that can display verification codes, you can have a code sent to your trusted phone number via text or a phone call instead. Click Didn't Get a Code on the sign in screen and choose to send a code to your trusted phone number. You can also get a code directly from Settings on a trusted device.

I believe Apple prefers that people use a trusted device as from their point of view this is more secure as they can verify the entire communications loop so they view this as a fallback option, but you certainly can use non-Apple devices to authenticate. They also don't appear to throw up any roadblocks to doing so.

Isn't the fallback only SMS/phone? That seems like a roadblock compared to say Google Authenticator.

Actually the new 2FA method they introduced somewhat recently does allow this.

Also, you're forced to use silly old password reset questions (from a predefined list). I just recently had to do this for my dev account (not Apple user otherwise) and was mildly shocked. There were no questions people knowing me couldn't answer with moderate research effort...