The mantras you refer to in devanagari are
ॐ सरस्वत्यै नमः, ॐ श्रीलक्ष्म्यै नमः, ॐ उमायै नमः, ॐ नमो भगवती
OM Sarasvatyai namah, OM Srilakshmyai namah, OM Umaayai namah, OM namo Bhagavati.
It seems a constructed mantra, ie not from any scriptural source.You mention in comments that you got in introduction of an edition of Devi-Bhagavatam.
The third mantra referred to you is offering pronam to Umaa.Umaa is another name of Parvati, the wife of Lord Shiva.
The name of Uma is mentioned in Kenpoanishad (3/12):
sa tasmin eva aakaashe stiyaam aajagaama vahushovamaanaam umaam haimavatim : He saw in that very sky a very beautiful woman form of Haimavati Umaa.
According to Sri Adi Shankaraacharya, Uma is the name of Parvati, the daughter of the Himalays
himavato duhita haimavati
The great poet Kalidas says that Ma means 'Do not' and 'U' means 'go'. When Mother Parvati was going out of home for doing penance to have Lord Shiva as husband, Her mother requested Her : Don't go (U-Maa) and so Parvati was named Umaa henceforth:
Umaa iti matraa tapaso nishiddha paschaad umaa-aaakhyaam sumukhi jagaama.
Another view is that U-M-A is just a different cobination of the letters A-U-M and UMA is Brahmavidya Paraa-Shakti.
The last mantra offers pronam to Goddess (and is in incorrect sanskrit, as with 'Namah', chaturthi vibhakti has to be used as per sanskrit grammar, and it shouod be 'Bhagavatyai'.
Bhagavati is the female form of 'Bhagavan'. So it means the Mother Goddess.According to Sri Sri Chandi, Bhagavati is beyond three gunas.She becomes Lakshmi in sattva-guna, Srasvati in rajo-guna and (Uma or Parvati or) Kali in tamo-guna.
Devi is the female form of 'Deva'. Devi literally means 'shining'.
Hope this addresses your query.