Hello, 

As per your question, i would say that there is no 3rd phase round  of counseling for ap eamcet 2019. If you have got your college already as per your rank, you have to take admission there only or again wait for next year exam, appear it and score more marks and get your preferred college. This year you can only get admission in your alloted college as no more round of counseling is left. 

In 2nd round which is the last round of counseling, getting a seat will depend on

factors like student to seat ratio, caste, your rank and marks, no of students applying this year in that college , etc.

For more details please check, 

Https://engineering.careers360.com/articles/ap-eamcet

Good luck