Moving a line - home office business

Howdy!

I'm new, just had the Deluxe 25 package installed for my home office internet needs.  Everything works okay, except a VoIP phone supplied by my employer (AASTRA 6757i).  It cuts out (I can't hear my clients, my clients can't here me) for a few seconds on a call.  The phone also just sit and drop connection in general.

I did several things, and unfortunately it's of my own doing.

I connect most of my devices by powerline adapters through the house (uses the house's main electrical wiring) or use WiFi.  The cable modem supplied by Comcast is in the basement, but the home office "room" is on the second floor.  The VoIP phone is connected to a hub connected to powerline adapters.

Comcast suggested I try a faster connection temporarily, and now I have the Deluxe 75.  The phone cutting in and out problem didn't get fixed. 

So just as a test, I got a 100-foot CAT6 cable and ran it down the stairs into my basement and attached the phone directly to the cable modem.  That seems to have done the trick.  That, and also my speed doubled on all my devices did as well (went from 41 Mpbs to 87).  But I can't leave the cable out in the open in the stairway, across an open floor where pets and dogs can trip, obviously.

On one of my earlier calls, Comcast suggested I place a call to move the line connection from where it currently runs to a point closer to my office.  That will cost about $120.  I'm just wondering if there's a simpler solution to get the cable modem "more directly" attached to where my home office is up two floors.  WiFi, even with an extender, still has the sound cut outs.  Powerline connections definitely aren't the way to go.

If any of y'all have suggestions beyond the $120, I'd be eager to listen.  I'm not being cheap, I'm just not sure if there's some other solution I haven't figured out yet.

Thanks!

Mark