How does a hydrophobic environment help in bond formation?
The major reason of the ‘hydrophobic environment’ is to block the enzyme-complex from accessing the solvent (water), which might otherwise enter the active site and hydrolyse ATP.

The reduction of polarity also helps to speed up the subsequent nucleophilic substitution. 

Note: Hexokinase is a soluble, cytosolic protein

The reasoning behind this statement comes from the X-ray structural studies of yeast hexokinase (HK) by Thomas Steitz.


  Comparison of the X-ray structures of HK and the glucose–HK complex
  indicates that glucose induces a large conformational change in HK.
  The two lobes that form its active site cleft swing together by up to
  11.5 Å so as to engulf the glucose in a manner that suggests the closing of jaws.


This movement places the ATP in close proximity to the group of $\ce{-C6H2OH}$ glucose such that water is sequestered from the active site. 
Water is certainly small enough to fit into the phosphoryl acceptor group’s enzymatic binding site. Moreover, phosphoryl transfer from ATP to water is more exergonic than it is to glucose.  If the catalytic and reacting groups were in the proper position for reaction while the enzyme was in the open position, ATP hydrolysis (to yield ADP + Pi) would almost certainly be the dominant reaction.

However, the large conformational change of the enzyme induced by glucose causing the exclusion of water from the active site making the phosphorus atom more accessible for the nucleophilic attack of the C6-OH group of glucose ensures that HK catalyses the phosphoryl transfer to glucose rather than ATP hydrolysis and also reduces the polarity of the active site, which help accelerate the nucleophilic reaction process.

This substrate-induced conformational change in HK is responsible for the enzyme’s specificity. 

References


Lehninger Principles of Biochemistry
Voet and Voet Biochemistry