FWIW, I think you are fine with what you have Mike. The #14 speaker wire would be fine for power and phone wire ok for switches. I don't know what gauge phone wire is, but maybe lights too, especially if they are LEDs. Regular old light bulbs may require more circuits or larger wire depending on loads. Everyone is correct about the solid wire, just be careful not to score or nick it when stripping. The smaller stuff may also be more prone to breaking if nicked? You can also score or nick stranded wire too and lose a few strands here and there. Not as bad as the whole wire breaking in two though. And you sure can't beat the cost of what you have.
I really wanted stranded wire for all my switches and lighting too, but ended up using thermostat wire from Lowes or Home Depot. It is #18 solid which is larger than phone wire, but I don't know by how much? I wanted to use #20 stranded, but could not find any multi-conductor that was readily available or as affordable as the thermostat wire at the home centers. The t'stat wire comes in 2, 3, 5, 7, 8 (or 9) and maybe more conductors, just about anything you would need. I thought the Cat5 network wire was just too small, but I believe some here have used it on their switches and things. I don't know it's gauge either, but I am guessing even smaller than phone wire?
Most of the stranded I found was also shielded which I did not want. I could have gotten what I wanted from my old employer that I retired from, they used a ton of it (#20 - 2 & 4 conductor stranded, no shield) and got a good price, but they had to order it and there were minimum quantities, etc., so Lowes\HD it was.
My solid wire is now in it's 5th year of operation with no problems so far. I also used your's and Tom Tee's method of colored tape to ID the different wires, just don't forget to note which one is which. I know someone that has done that, and on a train layout too! Fortunately he doesn't have a huge layout yet and he has promised to do better on any future additions!