Mehboob Khan, Kirklees Council’s Labour group leader, stepped down as his party’s national representative on the board.
The move came after the board confirmed it would look into complaints Clr Khan ran up the bumper bill on personal calls – including several to a friend in Uzbekistan – from a council office.
Clr Khan said: “This has been standard procedure in the past when board members have had allegations made against them.
“The appropriate thing to do is to temporarily distance yourself, so there can be no accusation of unfair dealings.”
He added: “I welcome the fact the Standards Board are looking into the allegations and hope that this will be the opportunity to establish the truth.”
BNP group leader Clr David Exley reported Clr Khan to the Standards Board after it emerged he had been using a phone in the Labour group’s office.
Clr Khan is repaying the bill at £100 a month.
A Standards Board spokesman said the fact it was investigating did not mean Clr Khan had done anything wrong.
He said: “This process is simply a case of establishing the facts. There is no presumption of the outcome.
“It is not a case of ‘there’s no smoke without fire’,” the spokesman added.
He said the case was being investigated at a national level, rather than at local level like other ones.
“Cases that are investigated at a national level tend to be more complex, involve a potential conflict of interest or require powers beyond those of the local authority,” he said.
The process will take about six months and there are several possible outcomes.
Investigators may conclude that no further action is necessary.
They may hand the matter to the council’s standards committee, which has the power to impose sanctions, including suspending Clr Khan from the council.
Or they may pass it to the adjudication panel for England, which has much more far-reaching powers, including long-term suspensions.
Clr Khan said he was confident his name would be cleared.
And he took a swipe at opposition councillors, accusing them of making political capital out of the investigation.
He said: “I’m annoyed that certain other politicians have used the fact that I’m not allowed to talk in detail publicly about this matter to smear me.
“I think they should refrain from making any comments until the outcome is known.”