AppleScript Dialog gives error

on run
    set cat to value of variable "cat" of front workflow (*I have already defined the variable elsewhere in the workflow*)
    set num to {}
    set myString to ""
    tell application "Contacts"
        repeat with i in cat
            set inGroup to group i
            set phoneProps to value of phones of inGroup's people
            repeat with i in phoneProps
                try
                    set myString to myString & "\n" & first item of i (*gets first number only*)
                on error
                    set myString to myString & "\n" & "blank field" (*covers for empty phone number, otherwise would halt on error*)
                end try
            end repeat
        end repeat
        return myString
    end tell  
end run

Try:

set searchText to text returned of (display dialog "Enter your search text:" default answer "")
set matchText to paragraphs of (do shell script "mdfind \"kMDItemTextContent == " & quoted form of searchText & "\"")
if matchText ≠ {} then
    set targetMatch to (choose from list matchText) as string
    if targetMatch ≠ "false" then tell application "Finder" to open (POSIX file targetMatch) as alias
end if