People hate computers. Computers are cranky, quasi-magical machines that can only be properly operated by mutant lizard people who have been genetically disinherited from the finer things in life, like meaningful social lives or mating opportunities.
But a phone... a phone is a social lifeline. In the 80s, it was a mark of privilege to get a phone -- even a regular, POTS, wired touch-tone phone -- installed in your room as a kid. The truly posh got their own phone lines. It meant you could keep in touch with your friends (or bf/gf) whenever you wanted. Themed phones (football, New Kids on the Block, etc.) were commonplace. This even extended into the cellular era with things like custom faceplates for Nokia dumbphones.
Technically you're correct. A smartphone is a computer. It has a CPU and RAM and can run programs and is indistinguishable from a computer in terms of its structure. But your technical distinction between "computer" and "phone" is as meaningful to most people as the technical distinction between "mammal" and "fish" would be to the ancient Hebrews, who called the whale that swallowed Jonah a "great fish". They classed everything in practical terms related to their own experience, under which a fish was anything that swam in the sea and had to be hunted or caught by people in boats.
To most a "computer" runs Windows or occasionally macOS and is used by students, office drones, and lizard people to crunch numbers or prepare documents. A "phone" is a tool for people with social lives to engage in and manage those social lives. From a perspective of what it's used for, it has a lot more in common with an office phone or a teenager's NKOTB-themed bedroom phone than it does a computer.