SQL update of grouped data with increments

[unix]

I have a table with columns for an [update value], a [date], [time], [phone number], and an integer autonumber/primary key column.I want to update the table as a set so that it groups the dates and phone numbers together (i.e., if 2 or more records have the same date and phone, then they're part of the "group") but then also puts a "1" in the earliest time record for that group, a "2" for then next earliest time record for that group, etc.Updating with just the count of the group proved easy, but I'm hitting a wall trying to figure out how to update each group with incremental values based on the time sort.