Great work Mollipops and Debra! It does appear that Joseph Packer was an alias of the convict John Roche. I found John Roche listed in the Ancestry Convict Database with an entry 'To S.A 6.11.1866'. (Presumably this is a typo and should read 1856 as Mollipops noted above)
http://search.ancestry.com.au/cgi-bin/sse.dll?MS_AdvCB=1&...

I presume my friend who is researching 'Joseph Packer' and Mary Egan would need to obtain all the certificates for the children of John Roches/Rochez/Roche and Mary Egan/Gagan to solidify the case that her ancestor was John Roche who arrived on the Phoebe Dunbar.

Thanks so much for all the leads you have provided here.