Does the PhpEd editor have a feature that allows you to mark lines and quickly return to them? For example, in most editors, on line 345, you can press a key combination such as CTL K 1 (not simultaneously, but in sequence), and mark the line for later return. Later, pressing CTL 1 will return the editor to line 345.

The number of lines that can be marked this way is generally 10, CTL K 0 through CTL K 9.

Of couse yes, PHPEd do support bookmarks.
Try Ctrl-Shift-<digit> to set and Ctrl-<digit> to jump to.
Alternatively, you can use Ctrl-K, <digit> to set and Ctrl-Q, <digit> to jump to.

All shortcuts can be seen and/or changed in Settings dialog on page "Editor Shortcuts"

Is that CTRL K simultaneously or CTRL then K?

Isn't it faster to just try it yourself?
Yes, "Ctrl-K" mean that you should press "Ctrl" and "K" simultaneously.