There are several ways to label individual phalanges.
You can say, “phalanx 3, digit 4 of the manus.” Not sure why, but people seem to put the phalanx first.
You can write in a caption, “ph. 3, dig. 4, man.” I’ve seen this dozens of times.
Or you can do what I’ve been doing lately, “m4.3.” And for the pes, “p4.3.”
If I’m starting a sentence with a phalanx, I’ll write “Manual 4.3…” or “Pedal 4.3…”
The old mc3 and mt3 still work for metacarpals and metatarsals.
Occasionally you’ll find a phalanx that is the product of fusion. Then it’s “m4.2+3.”
Of course, if a phalanx is lost, and you don’t want to skip a number on your way to the ungual (like skipping the 13th floor on a building), well, you’re on your own. Do the right thing in terms of context and consistency.
Simplify your captions and not only will you save space in your figures plus wear and tear on your keyboard, you’ll also make things easier to understand for the reader. Isn’t “m4.3” easier to understand anyway?
A modest proposal.