Remove the For Loop, and this code should do the job:
i=0
Do While (sr.Peek() <> -1)
line = sr.ReadLine
temp = line.Split(",")
ReDim Preserve memberData(i)
ReDim Preserve phoneData(i)
memberData(i) = temp(0) & "," & temp(1)
phoneData(i) = temp(2)
i += 1
Loop
The way you had it, the counter was increased only after you finished reading all the lines, that's why only the last entry was saved.