Union Query

Are you joining two tables? Or is it one table and you want to show the results from one table as one record with 3 numbers instead of 3 records with 1 number in the case of customer 1?

What is the purpose of this? Just for display on a form? I would use a For Next Loops probably. Or a recordset. Or both. Make a string and add onto it everytime it gets a new number.

To turn Table1 into Table2, you need to create a custom function with VBA, then create a "group by" query.  I think Richard has done videos for both topics.  Hopefully someone will point you to them.

The custom VBA function would look something like below.  It loops through a recordset of all the phones of the specified customer and create a comma-delimited string of them.  You need to know how to manipulate recordsets with VBA.  Richard may have a developer video for that too:

Function GetAllPhones(customer As Integer) As String
    Dim r As Recordset, s As String
    
    ' Create recordset of all phones for the specified customer.
    Set r = CurrentDb.OpenRecordset("SELECT phone FROM Table1 WHERE customer=" & customer)
    
    s = ""
    
    ' Move to first record.
    r.MoveFirst
    
    ' If last record hasn't been reached, run do loop below.
    Do While Not r.EOF
    
        ' If s is not empty, add a comma.
        If Len(s) > 0 Then s = s & ", "
        
        ' Append phone in current record to s.
        s = s & r!phone
        
        ' Go to next record.
        r.MoveNext
    Loop
    
    ' Return resulting string.
    GetAllPhones = s
        
End Function


Then you use the above function in a "group by " query:

SELECT Table1.customer, GetAllPhones([customer]) AS phones
FROM Table1
GROUP BY Table1.customer;

Dlookup Plus Function Developer 17

It seems that it is not union query

I just want to print Table 1 in a small label, it will be too tall to have phones line up like this

therefore I just want it to line up like Table 2 for easy label printing

Use my DlookupPlus function that Juan recommended.