Plexiglas is not a traditional part of a plasma screen. Plasma TVs use traditional glass with protective coatings for operation, not Plexiglas, which is a type of plastic that would hinder the clarity of the image and would not be able to interact properly with the gases. If you have the original Philips plasma screen, it cannot be replaced with Plexiglas, although the entire panel may be replaced with a new factory version to fix problems.
Plexiglas is seen on plasma TVs when owners add an extra layer of protection. Some companies offer thin Plexiglas covers that can be attached to the TV. This may be helpful if you are using the plasma TV in a family setting where damage is more likely, or simply want to protect your TV surface from cracks and bumps that would damage it, or to turn the TV into a mirror when not in use. In this case, the Plexiglas can be taken off and replaced if it becomes damaged itself. This is one reason the covering can be a useful protective option.
Plexiglas coverings are attached to plasma TV screens via connectors around the edge of the screen. Unbracketing these connectors with a screwdriver or by other appropriate methods is enough to loosen the Plexiglas until you can safely remove it. A new Plexiglas cover will fit into the same area and can be connected using the same fasteners, unless you prefer to switch to a new cover or style.
Plasma TVs can produce heat through the screen, which may be a problem if the Plexiglas is pressed too close to the screen itself. If your Philips TV produces high levels of heat, you may want to install additional felt pads under the lip of the Plexiglas to give it more room for airflow. Size is also important. Choose a new Plexiglas cover that perfectly fits your TV in both width and height. A number of size options are available.