First, welcome to our message board.
Hi - new here so thanks in advance for whoever may be reading this!
I was wondering how to apply the astrological phases to a natal chart.. such as where is the overlay applied, where does it begin (what house?)?
It begins with the slower moving of any two planets being considered. The distance from the slower moving planet and the faster moving planet then correlates to the phase that exists between them. For example, Saturn could be at 0 degrees Leo, and Mars could be at 01 degree of Scorpio. The phase would then be a 1st quarter phase. The 'overlay', as you put it, starts wherever the slower moving planet is located in the actual house of a chart and ends where the faster moving of the planet is located. So if Saturn, in the example here, is located in the 5th house, and Mars is located in the 8th house, that overlay then exists between these two houses.
Also if there are more than 2 planets in one given phase, what does that mean/how would this change an analysis?
Relative to phases only two planets are considered in order to determine the phase between them.
God Bless, Rad