Deciphering unknown scripts is insanely difficult. In fact, all of the big scripts started with use of a bilingual inscription: Egyptian via the Rosetta Stone, cuneiform via a bilingual Akkadian/Persian inscription, and Mayan via a (botched) bilingual alphabet. There's nothing of the sort for Indus Valley Script, and the texts themselves are too short for even cryptology to be of much use. It's not even clear that Indus Valley Script is true writing as opposed to proto-writing, i.e., if it was capable of encoding full utterances within the language spoken of the time.
The link between the Phoenician abjad and the Greek alphabet is quite well-attested, not least of which is the order, shape, and phonetic correspondence between the letters is damn near perfect. Compare the correspondence of Phoenician and Greek versus Linear B and Greek, say. It takes pretty big blinders to say the Greek alphabet couldn't have come from Phoenicians.
"Merv is the oldest and best-preserved of the oasis-cities along the Silk Route in Central Asia. The remains in this vast oasis span 4,000 years of human history." - http://whc.unesco.org/en/list/886
indus script dates back to nearly the same as sumerian and egyptian around 3200 bc with some potsherd markings dated further back to 3500 bc
if indus script was related to sumerian it wouldnt be undeciphered till now
the first evidence of brahmi is from lanka which is probably as far from levant as china
it is funny that the intrusive nature of the alphabet amidst the syllabaries is not remarked upon but just accepted especially since the other intrusive party of the time 1500 bc are indo europeans and most likely indo aryans in the mitanni and kassite eras
the near complete further non development of the alphabet to better fit the languages indicating the borrowed nature of it
as opposed to say brahmi or chinese
no mention of the tale that the phoenicians gave greeks the alphabet or dicussion of their origin which is still unknown herodotus or someone said they were of the african coast i believe ie not native but everyone pretends this is just fake
the strained efforts to relate everything back to egyptian heiroglyphs because europeans want that heritage too