Apparently, then, wikipedia is not really reliable concerning the date of construction of the Pharos. The only sources for it are the Suda (s.v. Pharos) which says it was built in 297 (the year Pyrrhos returned to Epirus) and Eusebius' Chronicle, dating it in 283/2. P.M. Fraser (
Ptolemaic Alexandria, Oxford 1972, I, p. 20) plausibly suggested that these might be the beginning and the end of the construction works.
The basis for the date wikipedia provides is probably the following statement later on in the same article:
The building was finished during the reign of his son, Ptolemy II Philadelphos
The source for this view can only be Eusebius' Chronicle, which, as said, gives the exact date of 283/2, the year when Ptolemy II succeeded to the throne. There is no reason to consider the whole of Ptolemy II's reign as possible date for the construction of the lighthouse.
regards,
abm