Phelps, who ended his glittering career after last year's London Olympics, amassed 26 world titles, while Lochte owns 12 ahead of the latest championships in Barcelona starting on Sunday.
It will be the first Phelps-free major competition in more than a decade and Lochte told a news conference the 28-year-old Baltimore native, who will be in the Catalan capital as a spectator, would be sorely missed in the pool.
Lochte took a lengthy break after the 2012 Olympics, including appearing in his own reality TV show, but is still confident of at least a medal in the seven events, four individual and three relay, he is contesting.
"There's no doubt he (Phelps) is going to go down in history as the best swimmer ever and I was just happy I was a part of that," Lochte, who is also 28, told reporters at the US team's pre-competition briefing.
"He's the hardest racer I have ever had to go up against and I had fun and we grew into a really good friendship because of that," he added.
"We both pushed each other and now that he is gone I am definitely going to miss him.
"But I can't really focus just on him. There are other competitors out there who are finding different ways every year to get a lot faster.
"I just have to worry about myself, step on those blocks and race."
Some media reports have suggested Phelps may be preparing a comeback, something Lochte said he would welcome.
Phelps's former coach Bob Bowman, who is the head men's coach for the U.S. team, said he was unaware of any such plans.
"My answer to that is always when I see it I'll believe it," he told reporters.
"I have had no indications at this point in terms of him coming in swimming or showing an interest to get in any kind of programme so I think that's where we'll leave that one."
Missy Franklin, the standout performer in the U.S. women's team, was also asked about a post-Phelps world and the 18-year-old, who won four gold medals in London, said she and her team mates were trying to create their own legacy.
"I don't think anyone will ever fill his (Phelps's) legacy," she told reporters.
"He has just been such a bright light for all of us and it will continue to shine for years and years to come.
"There is really no filling in for his legacy it just speaks for itself and I think we all hope to have our own."
The all-powerful Americans are almost certain to top the medals table again in Barcelona, which would be the 13th time in 15 editions since the first championships in Belgrade in 1973.
Both Bowman and head women's coach Dave Salo said there was some exciting younger talent poised to break through alongside more established swimmers like Lochte and Franklin.
"I think our veteran squad is kind of running on their talent not so much their preparations as they did last year but they are pretty exceptional athletes," Salo said.
"It's a dynamic group of women and I think everybody is going to be battling for a podium position."
Bowman added: "Our men's team is a very interesting mix of some veterans who have established themselves on the world scene and for the first time in several years we have some young guys on the team.
"So we have a kind of a mixture of experience and youth which I think will be a lot of fun."
- Sports & Recreation