The Phoenicians got all the way to China? I didn't know that.
I tend to think that India will be more difficult for Alexander's army to conquer than Persia, for several reasons.
First of all, the Persian Empire was one huge political unit. Once you decisively defeated the large main armies and killed, captured, or completely discredited the ruler of such an empire, resistance would tend to weaken or even vanish in other areas, allowing you . India, on the other hand, was split into many warring kingdoms. Killing or capturing or humiliating the ruler of one kingdom is only going to give you control of that particular kingdom, it won't help with the other 20 or 30 that you have to deal with.
Second, Darius IIIs ability as a battlefield leader and tactician left much to be desired, to put it mildly. Had the Persians been led by someone of the caliber of Cyrus or Darius I, Alexander's task would probably have been much more difficult (not that it wasn't really difficult already). In India, some of the local rulers may have been poor or mediocre battlefield commanders, but others would have been tougher opponents. In OTL, the Indian ruler that the Macedonians called "Porus" (whatever his actual name was) seems to have been a much better leader than the Darius, and there might have been quite a few other leaders of equal or greater ability that Alexander would have had to fight.
Third, weren't there some diseases in India that Alexander and his men wouldn't have encountered, or wouldn't have encountered in as dangerous a form, before?
On the other hand, if anyone could take on this challenge, it would probably be Alexander and his army.