If its from a mobile phone – you might be in trouble.
Big prints (eg larger posters) tend to be printed at 154dpi so you can gauage quality from there- but thats assuming a reasonable camera and lens.
Someone will be along in a mo to suggest a way of inventing pixels but I’d suggest a max print size of 11 x 8.5 inches approx (assuming decent lens etc). Be aware that at bigger size other factors can make the print look poor too – focus, noise, small sensors etc.
If you want – email me the original and I’ll give more accurate guesstimate of what’ll look good.
I get prints done up to bus shelter sized ads from some odd sources – so you never know.