phase voltage is voltage between phase (R Y B) to Neutral.
& line voltage is Voltage between to phases like R & Y.
line voltage 415V.in star connection line voltage=phase
voltage*1.732=415v.

The voltage between line and neutral is called the phase
voltage. where the voltage between two lines called the
line voltage.
In star connection:
VL=1.732Vph

In delta connection:
VL=Vph
from above relation line voltage is obtain 415V in 3 phase
supply.

phase voltage is the voltage when any of the phase (r,y,b)
is considered along with the neutral and then the voltage
is considered this gives te phase voltage ,

line voltage is the voltage is is measured between any two
phase .

When you have multiple phases (lines with voltages having
different phase angles)there different ways of defining
voltage. Say you have 4 lines: Line A, Line B and Line C
and Neutral. Now let's say you have a "3 phase" source of
480V connected to these lines. Each line represents
a 'Phase'.

If you were to measure the voltage between, arbitrarily
choosing Line A and Line B, you would measure 480V. Now,
if you were to measure the voltage between Line A and
Neutral you would measure a much lower voltage. Namely,
480V divided by the square root of 3. This difference
shows that each 'line' is not actually carrying 480V. But
when you reference one non-neutral line with another non-
neutral line you get 480.

This is because you are referencing two voltage lines that
are out of phase with each other (in this case 120 degrees
out of phase). Therefore, the voltages will not be
in 'sync' and the differences will result in higher peak
voltages (480 in this case).

Line voltage is the potential difference between two lines of different phases. This means there are actually 3 line voltages on a three-phase system; A-B, A-C, and B-C. For a balanced system, the three must be equal.

Phase voltage is the potential difference between a line and neutral. A three-phase system has three phase voltages as well; A-N, B-N, and C-N. For a balanced system, all three must be equal.

For three-phase Alternating Current (AC) circuits, there is a relationship between line and phase voltage that is defined by the connection method (wye or delta).

For single-phase circuits (AC and DC), line parameters (current and voltage) are the same as phase parameters. This is because one leg is referred to as having 'potential', while the other is generally referred to as the 'return' or 'neutral' or 'ground'.

The conductors that connect the load to the supply are LINES (or 'line conductors', NOT 'phases'! Which is why the voltages measured between them are called 'line voltages'.

PHASES are not conductors, but the connections, such as individual loads (or the windings of an alternator or transformer) between line conductors, or between a line conductor and the neutral.

So 'phase voltages' are measured between lines (in the case of a three-wire system) or between a line and a neutral (in the case of a four-wire system).

So we measure line voltages BETWEEN lines, and we measure phase voltages ACROSS phases.