DP1-T Desk Phone Telo Multi-Line Setup

Hello, I hope I’m asking this in the proper section. I have one DP1-T desk phone, and three HD2’s connected to my Telo 2. My issues are that I’d like line #1 (my main home number), and my 2# to both be accessible though my DP1-T desk phone. I see no way to do this through MyOoma.com. What’s the point of having a 2-line desk phone I can’t utilize both Ooma lines from? Picking up a house call (my main line) while in the office on the DP1-T (my second line) without running to the HD2 in the next room is a big deal to me. Have I misunderstood or missed something here in setup? Has anyone successfully setup their DP1 to use their second line as default outbound and have the second line accessible on line 2 of the DP1 desk phone?

I’ve got the DP1-T that can be used with a Telo 2 without need of Ooma Office hardware, and this seems stupid I can’t use the second line.

Also, what’s the jack one the front side of the phone. It looks like a 3.5mm headphone or mic jack, but there’'s nothing in the manual about it. I do my headset plugged into the 2.5mm headset jack on the side that seems to work okay.

Any help is greatly appreciated. The included setup guide is horrible and doesn’t explain anything about any of this.