Welcome Juneeb. I suspect that there is a problem with the roots. Also, direct sun light is not safe for phals. They will prefer bright filter light. If the leaves get hot to the touch, be sure and move the orchid ASAP. One other thing - phals loose their bottom leaves as they age. They will put up another at the top. If the leaves continue to decline and you are concerned that it is not 'natural' leaf die back, then unpot this orchid and check on the roots.