Rank the Number of occurrence of phone number in the list

[nemypresbitero]

I have this list of repeat callers in my database. I have already determined the frequency of calls but I want to rank them according to the time of call. For example I want to put "1" as rank to the first call occurred in July 1 1:00AM and I want to put "2" as rank to the sencond call occurred in July 1 5:00AM and so on and so forth. I wan this to be dynamic and put in just one column. Help me please.