This phenomenological study explored the essence of the lived experiences of preservice teachers (PSTs) during clinical student teaching experiences as they reflected and described what they perceived as influencing sources on their teacher self-efficacy (TSE). The Teachers' Sense of Efficacy Scale (TSES) (Tschannen-Moran & Woolfolk Hoy, 2001) was used as a measure of general TSE. PSTs who had recently graduated from a private university were interviewed virtually using an artifact-elicited, semi-structured interview protocol. Data were analyzed using Transcendental Phenomenological Analysis (Moustakas, 1994) with In Vivo coding (Saldana, 2016) and Bandura's (1977, 1986) Social Cognitive Theory (SCT). Data included the demographic and contextual factors of PST participants and results added to prior research suggesting other sources of efficacy information (Morris et al., 2017) and nontraditional sources (Poulou, 2007) inform the development of PSTs' TSE. Four profiles, or patterns, emerged among PSTs and the unique ways they selected and interpreted meaning from sources contributing to the formation of TSE during student teaching. Implications, delimitations, limitations, and suggestions for future research are discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]