Buying a call in anticipation of a price rally is a bullish strategy.
When an in the money, at the money, or slightly out of the money call is purchased, the trader usually expects the price to rally.
There are some exceptions in which long calls and long puts are used to hedge a loss.
If the price of the underlying rallies and the strike price of the calls become deeper in the money, the trader can sell the option contracts and collect more premium than originally paid.
The amount of the price increase, the volatility, and the amount of time that remains in the option contract governs the amount of premium the buyer receives.
And you've seen how long calls that become in the money can be exercised and then sold for profit.