"After Vanessa [Bryant] lost Kobe, all I could do was look at Michael and be like, 'Can we please help you? Because if I lose you, I don't know what I'm gonna do'," Nicole said, in an interview with Today.
"Michael is the most amazing father and partner I could have ever asked for," she added.
The couple, who wed in 2016, have three children together: Boomer, 4, Beckett, 2, and Maverick, 16 months.
"Nicole loves me and wants to help. She wants me to get better," Phelps said.
"But she's struggling herself. She needs that support as well. I know it's hard for her."
The former professional swimmer has spoken candidly about the tough mental battles he's faced during the Covid-19 pandemic, including "some scary ups and downs", and the impact they've had on his family life.
"The boys want to be near Michael when he's having a rough day. They want to try and make him happy — especially Boomer, because he's the oldest," his wife explained.
"So we'll say, 'Hey Booms, Daddy's having a hard time and just needs to take a moment to be alone'. We want Boomer to understand it's not about him, it's about Michael."
To help her cope, she has also begun seeing a therapist.
"It's helping me with everything. It's support for me. But more than anything, therapy provides me with the tools to be able to help Michael properly," she said.
"We've definitely grown together through this and learned a lot. It's not easy, but I'm married to the most incredible human being."
She says she used to believe she could "fix him" but has now realised that is not up to her.
"I used to think, 'Oh, I can fix him. I can be his therapist. I can be what he needs'," she said.
"But what I've learned is that you can't take ownership for how they're feeling, no matter how badly you want to."
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.