They are already. I've got the Spacemit K3 and it is a bit below Sandy Bridge single-core speed - so nothing spectacular - but fast enough for everyday desktop use. And way faster than my old budget smartphone's SoC.

Yes RISC-V has not caught up to modern x86/ARM CPUs like Zen 5, Snapdragon or Apple but still fast enough for modern browsers and most software in general.

Already existing RISC-V CPUs are certainly fast enough to build entry level smartphones. It's probably just a matter of time (3-5 years maybe?) until some Chinese company does it.