Breakdown of Ich habe das gleiche Telefon wie du.
ich
I
du
you
du is informal, so don't use it with strangers, except if they are children. You might use it if your friend brings his buddies along, but generally we tend to first offer someone the right to use du with us.
wie
as in comparisons
haben
to have
gleich
equal; same
das Telefon
the telephone
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