Disclosing consideration for funded Master's during PhD program admissions As an undergraduate in the admissions process for a PhD program, should I disclose my status as a finalist for a separate and prestigious fellowship that would fund a Master's program? (I have already completed my applications, so any disclosure would occur after having been made an offer by a PhD program.)

If so, when is the appropriate and responsible time to disclose this information? 

Importantly, if I were to receive the MA fellowship, I would certainly accept due to its prestige.

My concerns are twofold:

1) I do not wish to lessen my bargaining power by disclosing this information too early in the admissions process (i.e. during negotiations over PhD funding or prior to an official offer).

2) I do not wish to provoke the ire of admissions boards and department faculties by withholding this information until too far into the admissions process. Particularly because I intend to complete my PhD after the MA program, should I happen to be awarded the fellowship.

In terms of a timeline, notification for MA fellowship recipients will be made between March and late April. Most PhD programs expect a decision notification in April.
If we're talking about a program such as a Marshall or Fulbright scholarship, such awards are usually considered sufficient grounds to postpone enrollment while the fellowship is being pursued.

On the other hand, I wouldn't raise this possibility until it becomes an actual issue. You're introducing unnecessary obstacles in the admissions process that way. If an offer comes along from a school or one of these fellowships, you can deal with it then