Hello, I hope you are doing well

Yes, you are eligible. The entrance exam is open for post graduates, B. Tech/ B.E. Engineers and Ph.D. too for recruitment process in Scientist B rank.

Moreover if your Ph.D. projects have got something related to on going projects of ISRO, that would give you an upper hand. The promotion statistics are generally more in the favor of Ph.D. scientists due to their industry experience and their field applications.

Hope this helps