How/when to build retirement emergency fund

I am targeting retirement in 3 years, at age 49. I’ll have a long period where I’m entirely reliant on my portfolio, as I’m going to hold off on drawing social security and my pension for as long as possible. My biggest concern right now is if the market crashes around the time I retire and sequence of returns murders my portfolio or keeps me at my job for several more years. So, I’m thinking ahead to an emergency fund with 2-3 years worth of cash or equivalents.

My question is, how do I do it? Just chunk over a bunch of investments in my brokerage account? Slowly DCA out of those investments? Wait awhile (2 years out, 1 year out)? Or start redirecting savings above my 401(k) match towards cash?