Photocurrent measurements and the Constant Photocurrent Method (CPM) were used to carry out a spectroscopic study of epitaxial phosphorus-doped n-type CVD diamond films. Two optically active defect levels, XP1 and XP2, with photoionisation energy of 0.56 and 0.81 eV, respectively, found in previous work [1] are discussed in detail here. Comparison of CPM data with the activation energy of the carriers from Hall effect measurements suggest that the XP1 defect can be attributed to the P-related donor level. XP2 remains unidentified. Measurements carried out on a set of samples show that the XP2 defect is only present in some samples showing high resistivity. To study the electronic structure of the XP1 level, photocurrent measurements at low temperatures (liquid N2 and liquid He) were done, revealing a phonon-induced oscillatory photoconductivity. Two sets of minima are observed which allow an estimation of the position of the first two excited states of phosphorus. Also a comparison is made with results from FTIR measurements.