Right. Any kind of phone service from an internet provider will require a phone to be plugged into a special jack on the provider's "router" device. It won't involve wifi and won't use any old-skool phone jacks already in your house -- though I guess you could connect them if you're ambitious. We don't need our house to have a phone line, so we just use our cell phones, plus the wifi calling that WhatsApp (or similar) can do.
Note carefully that wifi is wifi, and isn't somehow different with fibra óptica service. However, a new provider of any sort will bring a different "router" device than you had before, so any change in wifi signal quality will stem from that fact. The new base device may work well with extra wifi points you already own (and how they're positioned), or not. ISP-provided gear is usually mediocre.
TP-Link gear is as good as any other, and probably better than what Telmex would provide. We have a couple of these in the mix:
https://www.amazon.com/WiFi-6-Range-Extender-Booster/dp/B088H2FCHL/
Nevertheless I'll probably run ethernet to the one on our mirador, since its "mesh" connection is shaky, and we rely on it to connect some Wyze cams when we're away. We're away now.
One thing with TP-Link -- which will point you toward their "Tether" phone app to do the setup -- is that by default it wants to have each extender create a separate wifi network name (a separate "SSID"). So if your base wifi network name is "Telmex_hoochiemama_1234," TP-Link might suggest an extender name like "Telmex_hoochiemama_1234_ext1," or some such. This isn't ideal if you have one house and want everything using one network name.
But TP-Link won't prevent you from setting the same name on your extender as the rest of the house uses, so I'd suggest doing that. Their preference for discrete SSID names seems intended to reduce tech support calls.
Also, if you're experimenting with different extender locations, don't be shy about factory-resetting the extender (often with a paper clip) between attempts. It's often best to start fresh.
LQ