TL;DR Almost every phone today is digital for all (Mobile, VOIP) or most of the call path.
We think of phone calls as analog because they were for the first 100 years or so and because the human voice is inherently analog. But digital has tremendous advantages, whether for compressing on wires between central offices (24 voice channels on a T-1, and it goes up from there) or on the airwaves (available radio spectrum is limited).
Wired
In ye olden days, wired phone service, a.k.a. POTS, was strictly analog. Decades ago the vast majority of the internal phone network was digitized but with all analog/digital and digital/analog conversion handled by the telephone company in the central office. Some modern wired phones are often Voice Over IP (VOIP), which has the A/D and D/A conversion in the phone. Some use either fiber or coaxial cable with conversion in a "magic box" provided by the telephone or cable company that handles the A/D and D/A conversion so that you can use traditional analog telephone equipment (phone, answering machine, fax). And some still have a copper pair of wires going back to the central office, where the phone company handles A/D and D/A conversion.
Mobile (Cellular)
The first generation of cellular phones, now called 1G (it wasn't 1G when it was invented - just like Word War I wasn't "I" until there was a "II"), was based on analog transmission of voice, with digital transmission used only for some signaling purposes but not for voice. That required a lot of power and used a lot of spectrum (though there weren't that many phones/users initially, so that wasn't a big deal at first). 2G, which went into use starting in 1991, is entirely digital. 1G has been almost entirely phased out - I found one indication that there is still a 1G network in part of Russia. 2G is still available on many networks, despite the available of 3G and 4G for many years and the recent rollout of 5G, with each new generation providing higher data transmission speed and other advantages.
