The "opd." is short for "opened". It means (I think) that an existing grave was opened for an additional occupant, rather than a new grave started. If that was Phoebe's brother, then it would seem quite likely that it could have been opened again for her. Unfortunately, the transcription of the Abbey Cemetery records currently used in FreeREG finishes in 1908. James is actually the last entry. The cemetery remained in use, we just haven't got copies of the later records.
However, the James Allen who died in Bath in the last quarter of 1908 was recorded as 70 years old. If Phoebe's brother was born in 1819 he'd have been 89, so it is unlikely that this is the same James.
Alfred Street was in the Walcot district of the city. I'm not sure which parish, but certainly not the Abbey parish. So Phoebe would not have been automatically eligible for the Abbey Cemetery. She may still have been buried there if she was a regular at the Abbey church, but if she was a Presbyterian that would seem unlikely.
Well before 1910 all of the central Bath parishes had closed their original graveyards and were using new cemeteries on the edge of the city, usually with sections for non-conformist residents as well as Anglican parishioners. FreeREG does not have the records of most of these cemeteries. However, Bath RO does have an index covering a large proportion. See
http://www.batharchives.co.uk/burial-indexesIf you phone or e-mail them I expect they would look up Phoebe for you.
David