What is the meaning of St. Benedict's phrase "To work is to pray?"

The Benedictine motto is actually the command "Pray and work!" There can be a sense in which work is prayer if it is offered in a spirit of recollection and if prayer accompanies work or at least precedes or follows it. But work is never simply a substitute for prayer. Benedict was very clear on this. In his holy Rule, he teaches that nothing must take precedence over the true work of the monastery, which is sacred worship in the liturgy, which he calls the "Work of God".

Prayer to San Benedetto
O Holy Father Benedict, help of those who turn to you: welcome me under your protection; defend me from all that threatens my life; obtain for me the grace of repentance of the heart and true conversion to repair the sins committed, praise and glorify God all the days of my life. Man according to the heart of God, remember me before the Most High because, forgive my sins, make me stable in the good, do not allow me to separate from him, welcome me into the choir of the elect, together with you and the host of Saints who they followed you in eternal bliss.
Almighty and eternal God, thanks to the merits and example of St. Benedict, of his sister, the virgin Scholastica and of all the holy monks, renew your Holy Spirit in me; give me strength in the fight against the seductions of the Evil One, patience in the tribulations of life, prudence in dangers. The love of chastity increases in me, the desire for poverty, ardor in obedience, humble fidelity in the observance of the Christian life. Comforted by you and supported by the charity of the brothers, may I serve you joyfully and victoriously reach the heavenly homeland together with all the saints. For Christ our Lord.
Amen.