You could add some spaces with either the Space or String function.

Space
    X: [FirstName] & " " & [LastName] & Space(50-Len([FirstName] & " " & [LastName])) & [Phone]

String
    Y: [FirstName] & " " & [LastName] & String(50-Len([FirstName] & " " & [LastName]), " ") & [Phone]

Note: In my example (screenshot) I have used Courier New (Monospaced Font) so the phone numbers are aligned correctly.

Thank you Kevin,

How would you format it, if we need to keep the fix width of the text field, example [First Name] should have 25 char, if the record is less than 25 char, then it should have space, to keep the total number of char to 25.

Figure out it's LEN and then add that many additional spaces to it. (25-Len)

The problem I am getting with Space and Len is that when the field is null it display #Error in query and #Type! in report. I want it to put a number of space if the field has no value. I concatenated fields below and I have 3 records, but the last 2 records doesn't have costcenter, so it display #Error in query and in report it shows #Type!. I want the query and report to keep the number of spaces for that field.

"2" & ([GLNo1]) & Space(10-Len([GLNo1])) & "s" & ([DebitAmt]) & Space(23-Len([DebitAmt])) & ([Fund]) & Space(10-Len([Fund])) & ([CostCenter]) & Space(10-Len([CostCenter]))

SapiText                                                                GLNo1       DebitAmtFund        CostCenter
22512080   s113                    100000    19141612132512080113.001000001914161213
#Error                                                                25120802.00        1869
#Error                                                                251208084.001845

Use the IIF Function.

Using my previous example:

X: IIf(Not IsNull([FirstName]),[FirstName] & Space(20-Len([FirstName])),Space(20)) & IIf(Not IsNull([LastName]),[LastName] & Space(20-Len([LastName])),Space(20)) & IIf(Not IsNull([Phone]),[Phone] & Space(20-Len([Phone])),Space(20))

Thank you.

The Space()worked, but can you also do Format() with Space() to right justify it? How do you do it? - Thank you.

If you want it to have a right justified appearance simply put the Space() function BEFORE the Field name.