Electronic – How to make a PLL output the phase modulo 360°

IMPORTANT: the transfer function is an abstraction that tells basically what is the difference between the output (generally speaking) and the input (same as before); it's often used with voltages, but you can use what you want (also ice cream / fruit).

Then, just use the definition: as a Phase-Locked Loop (PLL)...

is a control system that generates an output signal whose phase is related to the phase of an input "reference" signal

...that ratio tells you what will be the phase of the output signal given the phase of the input signal.

The phase is well explained in the race car analogy: if you consider a sinusoidal signal as a dot going around in the euclidean circumference (counter-clockwise), the phase is the difference (in radians) between two signals (two points) in this circumference; or, for a signal, the distance from the 0 (rightmost point) of that circumference. In a more concrete way, is the "time" that has passed since when the signal has been the last time at value 0 while raising.

Since PLLs are circuits that try to synchronize clocks or signals in general, the phase is a good indicator of how much these signals are synchronized.

The Digikey summary table is a generic list trying to show all things to all men. Just ignore it and read the data sheet. Do not rely on it. Same with Farnell - they have a table/list for each component they list - go straight to the data sheet unless its the very basic info you're after.