JAM

Go onto the IIT JAM organizing institute website and then from their download the IIT JAM economics syllabus.

To give IIT JAM examination in a specific subject one must have studied it for four or six semesters depending upon the paper that one choose. Different subjects have different eligibility criteria. I would recommend, to go onto the official IIT JAM organizing institute website, and then from their download the admission brochure. All details are given in it.

For students having reservation under OBC category can get admission in IIT (Indian institute of technology), if they have secured rank under 1000 in IIT JAM examination.

To give the IIT JAM exam, 3 years gap will not any hurdle.
Yes, you or anyone can still give an exam with a gap after the bachelor's degree programme. But if you clear the TIFR exam then they might ask you for such a long period of gap after the Bachelor's degree programme, ( during the interview ).

For OBC candidates if they have ranked within 2000 in IIT JAM exam Physics then they have a chance of getting into IIT. With rank 2530, it will be better to opt for Central University of Rank. ( Admission will not be based on IIT JAM Physics rank ).

According to eligibility released by IIT JAM in year 2022, all that you need is to have passed the Bachelor's degree programme. Two years gap won't effect. In fact, there are many students who takes more than two years break for IIT JAM preparation. So, yes, you can apply for IIT JAM examination, just prepare well.

You need to give TUEE and institute's own entrance exam. JAM exam is not enough. Some of the institutes are-
Indian Institutes of Technology
Bhilai
Bhubaneswar
Bombay
Delhi
Dhanbad
Gandhinagar
Guwahati
Hyderabad
Indore
Jammu
Jodhpur
Kanpur
Kharagpur
Madras
Mandi
Palakkad
Patna
Roorkee
Ropar Tirupati
Varanasi
And IISC

To prepare for any of the jam exam
1. Get through the syllabus
2. Collect coaching and handwritten notes
3. Complete the syllabus atleast 1 month before the exam
4. Revise the syllabus and make short notes
5. Give mock test , so that you can know how well you have learnt the concepts.
The last month should be utilised only in revision not in new concept learning.

To SEE that go to official IIT JAM portal, then SEE the list of admitting institutions and courses offered by them.

Every year various IITS and participating institutions conduct IIT jam exam for various papers.
Every candidate has a option to opt for maximum two papers depending upon the shedule. THE papers one chose must be in different shifts. However it is completely optional to choose two paper.
Most of the students chooses only paper.
So yes you can take only Ph.