John was 24 years in 1916, born SA.  Only birth that 'matches'.  He is John Albert on his marriage registration and electoral rolls however her is Albert John on his attestation papers.  There is no birth for an Albert 
PHELPS in SA c1884.
PHELPS John
17 Jan 1884
Father Philip PHELPS  Mother Elizabeth MOUNTSTEPHEN
At Templers   Bar 319/70
Australian Electoral Roll
1916
PHELPS Annie Louise 196 McDonald Street, Kalgoorlie  HD  [original address in John's attestation papers]
and at the same address
PHELPS Oscar William, 196 McDonald Street, Kalgoorlie  Jockey
No enrolments until.....
1931
PHELPS Annie Louise 191 Newcastle Street, North Perth  HD
PHELPS John Albert  191 Newcastle Street, North Perth  Motor driver
1936, 1937, 1943, 1949, 1954
PHELPS Annie Louise 234 Stirling Street, North Perth  HD
PHELPS John Albert  234 Stirling Street, North Perth  Motor Driver
1958
PHELPS Annie Louise 194 Stirling Street, North Perth HD
PHELPS John Albert  194 Stirling Street, North Perth  Motor driver
1963
PHELPS John Albert  194 Stirling Street, North Perth  Motor driver
1968
PHELPS John Albert 238 Beaufort Road, Perth  No occupation
Buried at the same location as Beatrice Louise - his age may not be correct - different to year of birth at WW1 enlistment
http://www2.mcb.wa.gov.au/NameSearch/details.php?id=KB00142840You have their dates of death from the cemetery records and perhaps their death notices may be helpful.  I suggest you ask the State Library of WA for copies of notices if available.
Of course their 1915 marriage cert would list names of the bride and groom's parents but certs are quite expensive in WA.
Cheers 

Cando