Hi,
it's a delta load so you have to multiply the formula of active power P by root of 3 because the delta load is subjected to line voltage.
P=√3*VL*IL*cosθ
for me the whole procedure of the text is correct.
in fact, phase current = line current (in this case for delta load)
***it's a typo
correction: phase current= line current (in wye load)
phase current = IL/√ 3 (in delta load)
18.04 A (line current)
the line current leads the phase current of 30 ° angle
***correction: the line current lags the phase current of 30° angle (balanced load)
Regards