Using the same ESP8266's GPIO for 3.3v and 5v
So you want to connect either 3.3V sensors OR 5V sensors to the (one) RJ11 connector? In that case, for 3.3V sensor, I suppose you also want to provide 3.3V power instead of 5V power?
My solution would be to leave the level shifter in place, and (only) jumper the power at the RJ11 side between 3.3V and 5V.