Try this:
1. Join from table 1 to table 2 on ID.
2. Group on table1.ID
3. Create a formula to concatenate the phone numbers. It will look something like this:
StringVar Phones;
if OnFirstRecord or {table1.ID} <> previous({table1.ID}) then Phones := '';
If Phones = '' then
Phones := {table2.phonenumber}
else
Phones := ', ' + {table2.phonenumber};
Phones
4. Place your fields in the Group Footer for the ID group, using this formula for the phone number column.
-Dell