Regarded as one of the most prolific crime writers of the 20th Century, Wallace's gripping tales are considered the bedrock of the modern thriller, with The Case of the Frightened Lady being one of his most celebrated works.
And while Harry Potter presented many exciting twists and turns, Phelps is eager to dive into a new role that promises to keep audiences guessing.
"When I read the script, it kept me guessing right to the end - that's the sign of a great story," he explains.
"There's nothing more boring than going to see a whodunnit and realising who did it early on, but this play certainly doesn't give you that."
A new challenge
Set in the 1930s, the play follows the story of an Inspector Tanner who is called on to investigate a ruthless murder, with Phelps taking on the role of a young detective who assists in the case.
Phelps is certainly no stranger to performing, but making his professional stage debut presents a whole new challenge - one that he is especially eager to take on.
"It's something I've not done before, which I'm really excited to be able to try," he says.
"The way I see it, if you want to be taken seriously, you've got to be able to do theatre.
"I know I need to prove that I can perform live in a theatre, but I love that sink or swim challenge and I'm sure I'll find there's no better place to sink or swim than on the stage."
Heading into the unknown
Having begun filming Harry Potter from a young age, life on set was like working with family - literally so in the case of Phelps, who always had his twin brother James in tow, who played the role of Fred Weasley.
Now without the comfort of familiarity, the daunting task of going it alone is one that he has quickly embraced, despite fears joining The Classic Thriller Theatre Company would be like a "first day of school" situation.
Keen to prove his worth as an actor, Phelps hopes his appearance in the production will also help to attract a new slew of audiences into the theatre.
"If people want to come and see someone who was in the Potter films, but they enjoy the experience and it brings them back for another show, then that's a great reason to do this," he explains.
"Theatre engages with people, not just on the story front but with the whole experience of going in person and not being sat on your own.
"When I saw the show a couple of weeks ago, it was fantastic when the interval came down, as the first thing you see is people turning to each other and discussing it."
But while live theatre is a whole new ballgame for the Potter star, he does have plenty of experience of the touring life from his filming days and he's looking forward to getting back out on the road.
"When I was filming the Harry Potter movies, I virtually lived in a hotel room for nine months of the year, so I know how it can be," says Phelps.
"You can just sit down and do nothing the whole time, and it's the worst when someone asks, 'what did you do?' and you say 'I don't know', which I have been guilty of doing before.
"I'm taking my golf clubs and my gym bag, and I'm really looking forward to visiting parts of the country I haven't seen before."
The Case of the Frightened Lady will be at Leeds Grand Theatre from Monday 23 to Saturday 28 July 2018.