Phelps is on 51.05 per cent of the two-candidate preferred vote, ahead of Liberal candidate Dave Sharma by more than 1500 votes.
Electoral officials today were counting 511 postal votes, and a small provisional vote count was due to be held this afternoon.
It is understood the Australian Electoral Commission is not ready to declare the seat.
Processing and roll checking of arriving postal votes, pre-poll declaration votes, and provisional votes continues.
Meanwhile, Liberal frontbencher Christopher Pyne expressed confidence the party could win back the seat at a general election due by May 2019.
“There’s lots of examples of by-elections that have been lost by governments and then subsequently returned the following election – like Canberra, like the seat in Wollongong that was lost to the Greens by Labor during the Keating government,” Pyne told Adelaide’s radio FIVEaa.
“The important thing is politicians have got to stop talking about politics like it’s a parlour game.”
Local News Matters
Media diversity is under threat in Australia – nowhere more so than in South Australia. The state needs more than one voice to guide it forward and you can help with a donation of any size to InDaily. Your contribution goes directly to helping our journalists uncover the facts. Please click below to contribute to InDaily.