Why? AMD doesn't make phone chips, yet they're dominating Intel. Likewise for NVIDIA, who is at the top of the chip maker list.
The problem isn't what market segments they're in, the problem is that they're not dominant in any of them. AMD is better at high end gaming (X3D chips especially), workstations (Threadripper), and high performance servers (Epyc), and they're even better in some cases with power efficiency. Intel is better at the low end generally, by that's not a big market, and it's shrinking (e.g. people moving to ARM). AMD has been chipping away at those, one market segment at a time.
Intel entering phones will end up the same way as them entering GPUs, they'll have to target the low end of the market to get traction, and they're going to have a lot of trouble challenging the big players. Also, x86 isn't a good fit there, so they'll also need to break into the ARM market a well.
No, what they need is to execute well in the spaces they're already in.