Trainer Mark Kavanagh admits he lied when he told his owners he bought a second mobile phone during the cobalt saga because his son refused to speak to him otherwise.

But Kavanagh maintains he had nothing to hide in getting a new phone the day he learned of his cobalt positive for Magicool in January 2014.

Kavanagh admits he wrongly told his owners last December he bought it because his son, disqualified Sydney trainer Sam Kavanagh, would not talk to him otherwise.

He has now told his appeal against his three-year cobalt disqualification it was his wife Isobel who insisted he get a second mobile phone.

"My wife said I should do it because someone might be listening in," Kavanagh told the Victorian Civil and Administrative Tribunal on Monday.

Racing Victoria barrister Jeff Gleeson QC suggested Kavanagh bought the phone because he was not entirely innocent, which the trainer denied.

Gleeson: "The reason you bought the phone is because you had a lot to hide."

Kavanagh: "That's incorrect."

Kavanagh had told his owners he had absolutely nothing to hide over the second or "secret" phone after it was raised in his Racing Appeals and Disciplinary Board hearing.

"I bought the phone because my son (with whom it is now public knowledge I had a very strained relationship with) who lived in Sydney would not speak to me if I did not," he wrote.

Racing Victoria barrister Jeff Gleeson QC said that statement was a lie.

Kavanagh said: "It was incorrect, yes."

Gleeson: "It was a lie, correct?"

Kavanagh: "Yes."

But the Melbourne Cup-winning trainer denied deliberately lying to his owners.

"No, I didn't deliberately lie. It's what I believed at the time."

Kavanagh conceded his son's caffeine and cobalt positives came after the phone purchase.

Sam Kavanagh has told VCAT he was horribly offended and very upset by his father's lie about the second phone.

Mark Kavanagh told his appeal the vet at the centre of his own, his son's and fellow Flemington trainer Danny O'Brien's cobalt cases is a liar.

Brennan testified Kavanagh and O'Brien knew he was adding a substance called vitamin complex to drips given to some of their racehorses and each paid $3000 for three bottles of it, but none of them knew it contained cobalt.

Kavanagh has repeatedly denied paying Brennan.

He said he trialled an IV drip regime for delivering vitamins on Brennan's suggestion but stopped it after a month as it was not benefiting the horses.

Brennan has said Kavanagh said "stuff that, just use it" when told the vet could not guarantee the vitamin complex bottle's contents and testing would cost from $10,000 to $100,000.

Kavanagh said they were lies.

"When you employ a vet, they're told from the start that they do not have any unguaranteed products," he said.

A bottle of vitamin complex Brennan sent to Sam Kavanagh was found to contain high concentrations of cobalt.

Mark Kavanagh finishes his evidence on Thursday, before closing submissions for his and O'Brien's appeals during Melbourne Cup week.