PHOENIX — Neil Walker and his wife, Niki, are expecting their first child, a daughter, any day now. And for the Mets second baseman, who is determined to witness the birth, that means making certain concessions.

“I’ve pretty much got my phone on me everywhere except for at second base,” he said.

Even then, he’s got a backup plan in team trainer Ray Ramirez, who is responsible for relaying word in case Walker can’t be reached directly. At any moment during the Mets’ 10-game road trip, Walker intends to hop a flight back to his home in suburban Pittsburgh.

“It’s very exciting,” said Walker, who had three hits, including his 22nd home run, in the Mets’ 10-6 loss to the Arizona Diamondbacks on Monday night. “I wish we were in a place that was a little bit closer, but this is the hand we’re dealt right now and we’re going to deal with it.”

And for the Mets, that means waiting for the phone call that will mean going without their hottest hitter for as many as three days, the maximum absence permitted for players on the paternity list.

“We’ve been planning on it for a while,” manager Terry Collins said. “So we’ll put somebody else out there and move on, and he’ll be back in a few days.”

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However, Walker has become irreplaceable, thanks to a surge that has made him one of the hottest hitters in the big leagues. Entering Monday night, since July 27, he was hitting .444 with five homers and 13 RBIs. That average was the second highest in baseball during that span among players with at least 35 at-bats.

In that same stretch, Walker posted a .481 on-base percentage, fifth best in all of baseball.

Walker batted in the third spot in Monday night’s series opener against the Diamondbacks, further underscoring his importance in a lineup that still is missing Yoenis Cespedes.

“The confidence is where it’s supposed to be,” Walker said.

After a roaring start in April, Walker entered a two-month slump, with his average dipping to .237. Things got bad enough that Collins benched Walker for two games to allow him to clear his head.

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“He’s bounced back from it amazingly,” Collins said. “Right now, he’s a huge, huge part of our lineup.”

Walker, 30, has delivered a big season just before hitting free agency. In his first year with the Mets after his trade from the Pirates, Walker has hit 22 homers, one short of his career high in 2013.

The Mets have not ruled out retaining Walker for beyond this season. But that’s not what is on his mind at the moment.

If the call to return home comes while the Mets are in Phoenix, Walker should have access to a private jet, thanks to connections through his agents. He also has mapped out potential commercial flights that could get him back to Pittsburgh on short notice.

“You try to bottle up those three hours as much as you can,” he said. ”In between at-bats, I’ll shoot in here [the clubhouse] just to check my phone and make sure nothing’s going on. But there’s no control. This is a strange situation to be in.”

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As for what three days away might do to his swing, Walker has his priorities in order.

“I haven’t even thought about that,” he said. “Obviously, when you’re swinging the bat well, you want to continue getting as many at-bats as possible. But certainly, I’m not going to go blaming my newborn if I come back and don’t stay on fire.”