During the conversation, Bush backed Israel's demand that a ceasefire with Hamas take effect only after the rocket fire at Israeli communities end. However, the US president asked Olmert to make an effort to end violent clashes in the Strip.
Earlier Wednesday, the National Security Cabinet decided to continue the Gaza operation.
The White House spokesman said that Bush spoke with Olmert from his Texas ranch, adding that there is no point in a ceasefire that will not last.
The two leaders "discussed their mutual desire" for peace, presidential spokesman Gordon Johndroe told reporters.
"I think President Bush thinks that Hamas needs to stop firing rockets, and that is what will be the first steps, in a ceasefire," Johndroe said. "Hamas needs to agree not only to stop firing rockets now but to not fire any rockets in the future, stop smuggling weapons in, so they don't even have the ability to fire rockets, which also shows a good intent, that they don't intend to continue to target Israel. So I think they're certainly on the same page on that.
"President Bush wants to see an end to the violence. I know Prime Minister wants to see an end to the violence," the spokesman said. "We want to see a ceasefire that's durable and lasting and the most important thing is that Hamas respect it. They had a cease-fire until about Dec. 19 ... but then they failed to renew the ceasefire and substantially increase the level that forced the Israelis to live in bomb shelters."
"The onus is on Hamas," Johndroe said.
He added that officials are seeing "a good flow" of medical and food supplies into Gaza, addressing a concern that Bush raised earlier.