Bruce didn't say that 'the song was actually written by John Phillips'. Martin Parker wrote earlier than Phillips, so the lineage is more complicated than 'Artful Codger' (god, how I hate having to quote those ridiculous internet aliases. Why on earth won't people use their real names?) has assumed. For more detailed commentary from Bruce, and the text of the 'prototype', see http://www.csufresno.edu/folklore/Olson/:

The praise of Sailors, heere set forth

The reference (omitted above) to the file at Bodleian Library Broadside Ballads is Douce Ballads 2(167b).

See also Pepys Ballads:

Pepys 4.201: Neptunes Raging Fury
Pepys 1.420-421: Saylors for my money

There may be some relationship between this song (Roud 18526) and the much later 'Shepherd's Song' (Roud 284), but there is no clear connection beside the refrain; they are sung to different tunes, though the meter is the same.