Final answer:
The phrase expresses a gradual increase in temperature over a period of time.
Step-by-step explanation:
The subject of the question is English.
The phrase "It's been gradually getting warmer since last week" or "It's gradually gotten warmer since last week" expresses a change in temperature over a period of time. In this case, the temperature has been getting warmer slowly since last week. This is a common expression used to describe a gradual increase in temperature.
For example, if the temperature was 50 degrees Fahrenheit last week and is now 70 degrees Fahrenheit, it has gradually gotten warmer.