Phatak, a 1978 batch IAS officer of Maharashtra cadre, was the Brihanmumbai Municipal Corporation (BMC)commissioner and was chairing the high-rise committee, when some of the permissions were granted to the Adarsh Society.
"Almost 50 per cent of the investigations are over. We have gathered enough documents and records of the Society, which need to be scrutinised further. Phatak would be summoned anytime next week for questioning," a senior CBI official said.
Terming it as a normal procedure, the official said that all the accused would be questioned before the chargesheet was filed.
The FIR registered by CBI on January 29 this year says that Phatak, as the BMC commissioner, had approved the proposal to increase the building's height from 97 metres to 100.7 metres, on September 1, 2007.
The society is accused of obtaining a host of concessions, in breach of the local laws and Coastal Regulation Zone norms.
Phatak was the head of the committee for high-rise buildings, and CBI claims he did not seek opinion of other members of the committee when Adarsh's proposal came up.
Phatak's son, Kanishka, was allotted a flat in Adarsh in return for such favours, CBI says.
Phatak, at present an Additional Secretary in the Union Power ministry, has refuted the allegations saying that he was not posted with the BMC when his son was allotted a flat.