IMHO far too early. RISC-V processors aren't competitive yet. I suspect it is like this:

1. RISC-V instructions are simple and have short decode paths, meaning clock cycles could be faster, but

2. Higher frequency clocks create hard to deal with electromagnetical effects, so they can't do that

3. Instead they get low power, which is good for the phone, but not if the CPU is too slow.

4. They also can scale up to lots of cores

5. SiFive has done a lot of multi-issue out-of-order work to optimize their chips, but still not competitive for phones I think, and that kind of thing might lead to Spectre-like bugs.

There probably will need to be some kind of hybrid.