Not sure I interpreted correctly your formula, but in addition of the multline
environment, I nested it in the fleqn
environment, from nccmath
, which uses locally the fleqn
option from amsmath
, to ensure the multline starts at the left margin. Next, I used \splitfrac
from mathtools
(in medsize), and removed the *
symbols, which are not used in maths for multiplication, to save space – I just left the *1i
, because I have idea what they correspond to.
\documentclass{article}
\usepackage[intlimits]{amsmath}
\usepackage{mathrsfs,amssymb}
\usepackage{icomma}
\usepackage{mathtools, nccmath}
\usepackage{theorem}
\numberwithin{equation}{section}
\usepackage{commath}
\usepackage{bm}
\begin{document}
\begin{fleqn}
\begin{multline}\label{Equation 2}
Y( \delta_0,A,\delta_1,\delta_3,T_{\min} )= \Bigl(A_1\bigl(\delta_0\sin(\delta_0) + \delta_0\sin(\delta_1) + w\cos(\delta_3)*1i\bigr)\Bigr) + \\
+ \frac{\medmath{\splitfrac{%
\Bigl (A\exp(-T_{\min} \delta_0) \bigl(\sin(T_{\min} w) + \cos(T_{\min} w)*1i\bigr)
\bigl(\delta_0\cos(\phi - T_{\min}\delta_0)}{{} + w\cos(\phi - T_{\min} \delta_0)*1i +
\omega_0\sin(\phi - T_{\min}\omega_0)\bigr)*1i \Bigr)}}}
{(\delta_0^2 + \delta_1 w2i - w_1^{2} + \delta_0^2)\rule{0pt}{2.5ex}}
\end{multline}
\end{fleqn}
\end{document}

equation
to analign
construction. LaTeX does not auto break displayed formulas as that is very subjective and thus better left to a human.\split