Yes you can go to Bulgaria with romanian visa only for a transit and for a maximum stay each entry 5 days on your way to Romania.
To enter in Romania with a passport from Philippines you need the Romanian visa. See the links below for details.
no
NO.
no
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No
No you cannot enter without a valid Romanian Passport
A Romanian citizen can travel in European Union countries only with the ID.
list of visa free countries for bulgarians
yes you do.
It is highly doubtful.