Not necessarily. It depends on when Crystalline Giant entered the battlefield.
For example, in general, if Crystalline Giant entered the battlefield—
during your precombat main phase, its ability will trigger when your main phase ends and your combat phase begins (C.R. 603.2, especially C.R. 603.2c).
after your combat phase begins, or during a turn other than yours, its ability won't trigger until the next time a combat phase of yours begins (which will usually happen on your next turn).
Note also that Crystalline Giant's ability triggers "[a]t the beginning of combat on your turn"; thus it triggers each time a combat phase "of yours" begins, not just the first time a combat phase "of yours" begins while Crystalline Giant is on the battlefield. See also this thread.
For example, in general, if Crystalline Giant entered the battlefield—
Note also that Crystalline Giant's ability triggers "[a]t the beginning of combat on your turn"; thus it triggers each time a combat phase "of yours" begins, not just the first time a combat phase "of yours" begins while Crystalline Giant is on the battlefield. See also this thread.