I'm mid-beginner as a grower. I like the concept of pheno hunting but is there a realistic way to do it with a 2x4 tent in the basement?
Depends on what you are asking.
Can you find the best phenotype from 2-5 plants? Sure. Identifying the potent, vigorous plants, by side by side comparison is something most everyone can do. But 2-5 plants in a 2x4 is not going to give you enough examples from a complex cross or a polyhybrid cross to choose the obvious winners that stand out from runts and mediocre plants. Take a 100 genetic mish mash plants, and the majority will be mediocre, a small minority will stand out as better than average. Then what? Clone them? Spend the next 4-5 years stabilizing it? What is the end goal anyway?
Why not just grow a genetically stabilized sure shot winner in the same space? No choosing, using your resources and time filling up your available space with primo bud?
Is it really that 'cool' to grow unpredictable genetics with high degree of variation in potency, vigor, flavor/aromas, form worth it... just to say "I am pheno hunting" 4 plants at a time? No offense intended but... it sounds silly.
Just answer to yourself what is more important:
A full tent of high quality bud each time?
Or a bunch of mediocre unpredictable grows?