1) you can rewrite your transfer function T for s=σ+jω, then look at the limit for σ->0.
The transfer function -multiplying for its complex conjugate numerator and denominator- becomes
T(σ,ω)= ( 1+(σ^2-ω^2)LC - j 2σωLC ) /|T|^2
and for σ->0
T(0,ω)= (1-ω^2 LC)/|T|^2
as you can see this is always a real number (no imaginary part), it is positive for
ω<1/√LC
hence its phase is 0 and it is negative above the pole(s), hence phase is 180°
2) similarly its magnitude is
|T(ω)|=1/|1-ω^2 LC|
for values of ω much larger than the poles, the 1 in the denominator is negligible
|T(ω)|≈1/(ω^2 LC)
now if you represent this in a log log plot (take the decimal log of both sides)
Log |T(ω)|≈-2*Log ω + Log(1/ LC)
if you want to see this in dB multiply by 20 on both sides
20 Log |T| ≈ -40*Log ω + 20 Log(1/ LC)
which you see is a the equation of a straight line
Y = m X + q
Notice that 1/LC is the square of the poles, a number (much) larger than 1 in all practical cases in electronics, which means q is positive
This means the line has a slope of -40dB/dec and an intercept (intersection with dB axis, Y) at 20 Log(1/LC) dB
If you'd rather have the intersection on the frequency axis you can have it by setting Y=0 in the line equation
Log ω = Log(1/√LC)
the line crosses the frequency axis at the pole, as one would expect as this is GBW (the DC value of T is 1)