What is the "t" there?
It is there to make the liaison such as matayl already said. The liaisons are very important in french, as it is very complicated phonetically. With this particular example, if the liaison wasn't there, then there would be no way to phonetical distinguish between "parle-il" (does he speak?) and "par l'isle"(by the island). Phonetically, the "t" sound is very important in many scenarios. Another important one is with the word "est" (present 3rd singular of être). For example, when one says "il est bien", you pronounce the "est" without the t. However, if the est is followed by a vowel, such as in "il est alle", the est is pronounce like "e-t-alle"
It is an "epenthetic" t, added in just to separate the vowels and avoid a non-French-sounding pronunciation that would result without it (although it is actually the remnant of the 3rd person singular personal ending -t in Latin).
This case in French is explained under the heading "As a synchronic rule".