Not every phone supports eSIM. Most recent iPhones (iPhone XS and later) support it. Many Android phones do too: Samsung Galaxy S20 and newer, Google Pixel 3 and newer, and various other models. Before buying a UK eSIM from BuyUKeSim, check your device settings (e.g. Cellular / Mobile > Add Cellular Plan or Add eSIM) to see if eSIM is available.
How to check eSIM support
On iPhone: Settings > Cellular > Add Cellular Plan. If you see an option to add a plan by scanning a QR code, your phone supports eSIM. On Android: Settings > Network & Internet > SIMs (or similar). If you can add an eSIM or scan a QR for a new plan, you are good. BuyUKeSim sends a QR code after payment - just scan it on an eSIM-compatible device to install your UK +44 number.
For "eSIM compatible phones" or "does my phone support eSIM", check your model; then you can order a UK eSIM from BuyUKeSim with confidence.