Do LDS believe other churches to be the church of Satan? I was once informed by some LDS missionaries that other churches to them are the church of Satan? Is this an LDS doctrine or the view of some members?
Yes and no.
Yes
The LDS believe they are

the true Church of Jesus Christ, which was lost through apostasy, was brought back as it originally existed when organized by Jesus Christ 1

1 Nephi 13:1-9 mentions a great and abominable church and LDS manuals explain this with the following commentary:

“In relation to the kingdom of God, the devil always sets up his kingdom at the very same time in opposition to God” (Joseph Smith, in History of the Church, 6:364).
Elder Bruce R. McConkie (1915–85) of the Quorum of the Twelve Apostles defined the great and abominable church: “The titles church of the devil and great and abominable church are used to identify all … organizations of whatever name or nature—whether political, philosophical, educational, economic, social, fraternal, civic, or religious—which are designed to take men on a course that leads away from God and his laws and thus from salvation in the kingdom of God” (Mormon Doctrine, 2nd ed. [1966], 137–38).
One commentator explained that the great and abominable church consists of more than one entity:
“Actually, no single known historical church, denomination, or set of believers meets all the requirements for the great and abominable church: it must have formed among the Gentiles; ... No single denomination or system of beliefs fits the entire description. Rather, the role of Babylon has been played by many different agencies, ideologies, and churches in many different times. …
(Stephen E. Robinson, “Warring against the Saints of God,” Ensign, Jan. 1988, 38–39).2


No
While the LDS believe they are the true restored church they believe other religions and religious leaders have bits of the truth and were often important in the work of the restoration.
Some leaders mentioned in Preach My Gospel (the LDS missionary teaching manual) are: John Wycliffe, Martin Luther, William Tyndale, John Calvin, Buddha,
Confucius, and Mohammed.3
A principal teaching is a respect for other religions and beliefs:

I believe that we owe respect to all churches and organizations that lead men to act more righteously than they otherwise might, even if they don’t hold the keys of salvation and even if there is much error in their teachings4

and

The great religious leaders of the world such as Muhammad, Confucius, and the Reformers, as well as philosophers including Socrates, Plato, and others, received a portion of God’s light. Moral truths were given to them by God to enlighten whole nations and to bring a higher level of understanding to individuals . . .
Consistent with these truths, we believe that God has given and will give to all peoples sufficient knowledge to help them on their way to eternal salvation, either in this life or in the life to come . . .
Our message therefore is one of special love and concern for the eternal welfare of all men and women, regardless of religious belief, race, or nationality, knowing that we are truly brothers and sisters because we are sons and daughters of the same Eternal Father.5

and Article of Faith 13

13 We believe in being honest, true, chaste, benevolent, virtuous, and in doing good to all men; indeed, we may say that we follow the admonition of Paul—We believe all things, we hope all things, we have endured many things, and hope to be able to endure all things. If there is anything virtuous, lovely, or of good report or praiseworthy, we seek after these things.

1 https://www.lds.org/manual/preach-my-gospel-a-guide-to-missionary-service/lesson-1-the-message-of-the-restoration-of-the-gospel-of-jesus-christ?lang=eng
2 https://www.lds.org/manual/book-of-mormon-student-manual/chapter-4-1-nephi-12-15?lang=eng
3 https://www.lds.org/manual/preach-my-gospel-a-guide-to-missionary-service/lesson-1-the-message-of-the-restoration-of-the-gospel-of-jesus-christ?lang=eng
4 https://www.lds.org/ensign/1977/10/respect-for-other-peoples-beliefs?lang=eng
5 https://rsc.byu.edu/archived/selected-articles/god-s-love-mankind