Note that the end of the second word of the second line runs into the shoreline of the distinctively shaped island. It is by no means clear whether "insvla" is to be taken with the two words preceding on the same line, or instead with what is written on the line above.
ItMiller 393 reads this upper line as "Portus longus in Naxo insula", and regards Naxus as an otherwise unattested variant name for Ilva/Aethalia. I am less confident. "Port(vs)" is clear enough. I am tempted to read the next three letters as "lvi"; or possibly the number LVI ? There is then plainly a stop. After it "g", with a superscript following. The next three letters seem to be "iii"; or possibly the figure III ? Then, after a gap, "naxo". Hence: Port(vs) lvi. g-iii naxo.