Ptolemy I was mummified and his remains were placed in the Soma which was in the royal quarter of Alexandria, in fact most of the Ptolemaic rulers of Egypt were placed in the Soma or its expanded funerary complex. However the exact location of this mausoleum is unknown and the royal quarter of Alexandria along with much of the ancient city is actually underwater thanks to rising sea levels and the evershifting shape of coastlines. Then we have to also consider that many of the buildings and high profile tombs in Alexandria were looted, damaged or otherwise upset between Antiquity and today, with the mummy of Alexander himself being said to have been stolen, so there might not actually be anything left even if we did know where it was.