Phelps, 32, and his wife, Nicole, announced on Tuesday night the birth of Beckett Phelps, saying he was born on Monday.
"Magical moments yesterday," Phelps wrote on Instagram. "Nicole and I would like to introduce Beckett Richard Phelps to the world! We had a healthy baby boy and a healthy mama. I truly do feel like the happiest man in the world. Being able to build our family to now four (six with doggies) is so incredible!"
The ecstatic parents announced in August they were expecting their second child to compliment Boomer, who was born in 2016.
Last month, Phelps spoke at a mental health conference in Chicago where he talked openly about his almost life-long battle with depression and anxiety and is encouraging others to get help like he did.
Phelps also said he wants to eliminate the stigma associated with mental illness.