I would like to add a little more about this phrase.
The phrase الله أكبر is said to any situation that involved tribulation and hard ship, it is used to declare that no matter what the magnitude of hostile or danger or threat is one facing Allah is greater; the well of Allah is above and beyond any well for He is the supreme and ultimate power.
The phrase is also said in jubilation and cheering so it is not only limited to trials and tribulations and battles.
Also who ever say the phrase is indirectly announcing that the supreme power is to Allah, thus mean also a total submission.
The creator has 99 attributes and ONE name, surprisingly that name would not accept plural / feminine or any changes for example you can say GODS or GODEST or LORDS and in the matter of fact in English is enough for us to capitalize the L and thus mean that you mean deity.
Allah ~u Akbar is also part of the 5 prayers that starts and cover done time, noon time, afternoon time, sunset time and finally the evening time. So as you can read that phrase is very meaningful both in language and in rituals.