This fifth electron is squeezed into a higher energy state. In fact, at normal temperatures, heat can provide it with enough energy so that it can break it away from the core of the phosphorus atom and jump to a neighboring silicon atom. From there, it can jump to other atoms.
However, as the extra electron moves away, it leaves behind a phosphorus atom with 15 protons and neutrons, but only 14 electrons. The phosphorus atom thus has ionized to a net +1 charge. This +1 charge pulls on the -1 charge of the wandering electron and forces it to stay in the general vicinity.