{} is a limited quantity. What does the video example {a-z} mean?

Question

^php[5-7]{a-z}{2,5}, what is the explanation of this example? What does {a-z} mean? , does it mean that starting with php can only be followed by numbers from 5 to 7 in the range 2 to 5; or is it restricted to the beginning of php, which can only be preceded by numbers from 5 to 7