Fios using home phone plug

My Friendly fios installer used my home phone wiring to connect the gateway to my office using the phone line.

My problem is that I can connect only 1 local phone to the router/ gateway, but the phone/data line is being used by the fios. I want to use the home phone wiring for multiple phones- could I use a DSL splitter or something like that to plug the ooma back into the phone/ data port?

In a visual format:
current: (phone jack)---->(gateway)----->(ooma)---->(only 1 phone)
would this work?
(phone jack)---->(gateway)-----(ooma)---->(splitter)---->(back to the phone jack)—> (multiple phones)