Through vertical:

ABCDE

EDCBA

-

67866

obviously

A+E=6

B+D=6

C+D= 18, which leads to C = 9.

Then ABC can be divisible by 9, and A+B+C=A+B+9 can be divisible by 9, so A+B can be divisible by 9, and A+B must be =9.

comprehensive

A+E=6

B+D=6

A+B=9

Push A+B = 4+5 but not = 3+6 = 2+7. ...

Then DE = 2 1

Then push A = 5.

To sum up, this phone number is 5492 1.