T =
Use the sympref function to change the display of the symbolic polynomial:
I noticed that the string function does not update with this change(A = "x + x^2/2 + 1"), but it does if you use the latex command (B = '1+x+\frac{x^2}{2}') which may look better for plot headings.
syms x
T=taylor(exp(x),order=3)
sympref('PolynomialDisplayStyle','ascend')
A = string(T)
B = latex(T)
titletext = ("$" + latex(T) + '$')
title(titletext,Interpreter='latex')