Why might adding inorganic phosphate to a reaction mixture where glycolysis is rapidly proceeding sustain the metabolic pathway?

The addition of inorganic phosphate helps to sustain the reaction by helping the reaction to occur in a thermodynamically unfavorable manner.

Explanation:

The reaction  of inorganic phosphate with  glucose is an endergonic reaction which is thermodynamically unfavorable as a result reaction need coupling of ATP hydrolysis to take place in biological system because ATP hydrolysis releases huge amount of free energy as a result the overall free energy change of this reaction becomes negative which helps the reaction to proceed in a thermodynamically favorable manner.

       That"s why inorganic phosphate can be used to sustain the rapidly proceeding glycolysis pathway. The addition of inorganic phosphate makes the reaction thermodynamically unvorable.