Hi PG,
Leading or lagging is relative in many cases but the usual idea is to normalize to within a limit of plus or minus 180 degrees. Thus we would not say we have a phase shift of 190 degrees, we would say we have a phase shift of -170 degrees.
There are exceptions though, like when we talk about the three phase power line we usually say the phases are at 0 degrees, 120 degrees, and 240 degrees.
When we talk about electronic components though, there is a preference for labeling by how the component actually works when presented with a current or voltage such as a step or ramp (not just a sine wave). It becomes immediately apparent that the phase of the voltage lags the current or vice versa. For example with a capacitor, it is not considered possible to change the voltage of the device instantaneously so therefore the current has to come first which means the voltage has to lag. For the inductor it's just the opposite where we can not change the current instantaneously so the voltage has to come first and the current lags. To look at it another way, we can apply a large value of voltage (which means the voltage is there already) but we have to wait for the current to rise, so obviously the current lags.
The numerical value comes from the inverse tangent after considering the proper quadrant.
Long time ago before there were refrigerators people had "ice boxes". They had to wait for the guy who brings the ice to come to their house so they could replenish their ice and continue to keep their perishables cold. Somebody coined the phrase, "Eli the Ice man", which is kind of funny, but in capitals it reads:
"ELI the ICE man", in which ELI is short for voltage E leads current I for an inductor L (the E is before the I in ELI) and ICE is short for current I leads voltage E in a capacitor C.
If he didnt come that day i guess their food went bad and the electricians couldnt figure out the proper phase for their circuits that day either