We studied the exclusive reaction ep --> e' p' phi using the phi -->K+ K- d
ecay mode. The data were collected using a 4.2 GeV incident electron beam a
nd the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson N
ational Accelerator Facility. Our experiment covers the range in Q(2) from
0.7 to 2.2 GeV2 and W from 2.0 to 2.6 GeV. Taken together with all previous
data, we find a consistent picture of phi production on the proton. Our me
asurement shows the expected decrease of the t slope with the vector-meson
formation time c Delta tau below 2 fm. At <c Delta tau > = 0.6 fm, we measu
re b(phi) = 2.27 +/- 0.42 GeV-2. The cross section dependence on W as W0.2
+/- 0.1 at Q(2), 1.3 GeV2 was determined by comparison with phi production
at HERA after correcting for threshold effects. This is the same dependence
as observed in photoproduction.