Joe..Your Philo is really nice and very healthy.

Is the leaf on the left side dark...black/purple?

It could be P. 'Black Cardinal,' but I'm not 100% certain.

Are the leaves firmer than other Philos?

Why not Google, P. Black Cardinal, and P. Prince of Orange.
Leaves are too dark for Moon Light, which have golden foliage.

A new Prince of Orange leaf is orange, then turns green when mature. A Blck Cardinal's new leaf ir Red/black.

The problem with Googling plant pics online is, they post plants with a lot of coloring. Grown is perfect environment, more than likely the plant will have more than 10 orange or red/black, colored leaves. lol.
Growing indoors, chances are a plant might have a handful.

One other thing. Young specimens grow upright. As they mature, they vine. (Not all Philos.) Some start vining at a young age, others when Philos are 1' or taller.

Whichever species, your Philo is doing fantastic. Toni