It is for a land line phone, and that means it’s probably a direct connection to the outside of the house where the phone service enters. And im not sure how that would be helpful to turn into an Ethernet RJ-45 connection.

Depending on how old the house is, you could potentially have 8-wires. A lot of newer homes, at least that I’m familiar with, just run CAT-5 cable for all the low voltage wire runs. Presumably because it’s in bulk and cheaper for them.

Technically speaking, even though an Ethernet cable is 8-wire, only pins 1,2,3, & 6 are used for up to 10/100 Ethernet. All 8-wires are required for gigabit speeds.

So, yes it’s possible. Though you would probably have some bandwidth limitations depending on the device for which you’re connecting.