What is the correct MS Access expression within a form to return a value from one field related to another field in the same table?

I have a database of student travelers on an international tour. Each student picks three others as roommates, and I need to associate each roommate ( [R2] [R3] and [R4] ) with their respective contact phone numbers. I thought a DLookup function would work, but there seems to be an error.

=DLookUp("[Phone Number on Tour]","[June 2022 Travelers]","[Phone Number on Tour] = " & Forms("Rooming Roster")("[R2]"))

I can obviously create duplicate fields in the table to include the appropriate phone number associated with [R2], [R3], and [R4]; however, I'm trying to avoid having to duplicate field content.

Anyone have any thoughts on this?

Thanks in advance.